18 Ways Tertiary Si Shows Up in the Life of an INFP

If you’re an INFP, you’ve probably heard it all before: the dreamer, the idealist, the healer, the one with the heart too big for this world. People often describe you in glowing, poetic terms, but if you’re honest, you probably feel a lot messier than those descriptions. You have moments where your values burn like a lantern, guiding you through the storm. And then there are other times when you feel like you’re adrift in a dinghy with no oars, staring at the waves and wondering how you’ll ever get where you want to go.

At your best, you’re a mix of conviction and creativity. You see the potential in people, the hidden beauty in broken places, the spark of possibility in everyday life. Many INFPs I’ve worked with tell me that their deepest joy comes from helping people live authentically, whether that’s through counseling, art, writing, or simply being a safe, compassionate presence for the people they love.

But every strength has its shadow. Your compassion can turn into overextension, pouring yourself out for others until you’re exhausted and unseen. Your imagination can sometimes make you restless, always chasing new possibilities but struggling to bring them into reality. And your sensitivity, that beautiful gift, can also leave you vulnerable to harsh criticism or the weight of the world’s pain.

Still, the INFP’s power lies in this paradox: you are both fragile and fierce. Fragile in how deeply you feel, but fierce in how strongly you stand by your values. When you align your imagination with discipline, your compassion with boundaries, your authenticity with courage, you become a force that doesn’t just dream about a better world, but helps bring it into being.

I remember working with an INFP client who told me, “I feel like my insides are full of stories and ideas, but the outside world only sees someone who’s disorganized and behind.” She had poems stuffed in notebooks, art projects half-finished in her room, and a dozen ideas for community projects that she couldn’t seem to get off the ground. She felt guilty for being “too soft” and frustrated for not being more “practical.” But when we began to talk about her type, she realized something super important: her softness was her strength, and her creativity just needed structure. That realization became the start of her learning how to balance her natural gifts with discipline and boundaries.

Not sure what your personality type is? Take our personality questionnaire here. Or you can take the official MBTI® here.

The INFP Function Stack (For Beginners)

If you’re newer to personality type theory, you might wonder: What exactly makes an INFP tick? The answer lies in what we typologists call the “function stack.” Think of it as a set of mental tools that INFPs use to understand and process life.

Here’s the simplified version:

• Dominant Function: Introverted Feeling (Fi)
  This is the heart of the INFP. It’s why you have such strong values and an almost instinctive drive to live authentically. You measure life by what feels true, meaningful, and right deep down inside. Sometimes it makes you compassionate, seeing the heart behind peoples’ actions. At other times it can make you fierce, standing up for what you believe even when it rocks the boat.
• Auxiliary Function: Extraverted Intuition (Ne)
  This is your brainstorming superpower. Ne helps you see possibilities, patterns, and connections everywhere. It’s why you can take a tiny idea and expand it into a whole new world of creative potential.
• Tertiary Function: Introverted Sensing (Si)
  Here’s where things get interesting. Si shows up like a playful, childlike part of your psyche. It remembers details, rituals, and experiences from the past. Sometimes it shows up as nostalgia, comfort, or quirky traditions. Other times it can trip you up, making you cling to the familiar instead of taking risks.
• Inferior Function: Extraverted Thinking (Te)
  This is the part of you that wants order, efficiency, and measurable results. It’s not your comfort zone, but when developed, it helps you bring your big visions to life in the real world.

Every INFP uses all four of these functions, but Fi is the captain of the ship, Ne is the adventurous first mate, Si is the child onboard, and Te is the sometimes-bossy stowaway who can cause trouble—or save the day—depending on how you use it.

The Tertiary Function – Introverted Sensing (Si)

Now that we’ve looked at the whole INFP stack, let’s zoom in on the tertiary function—Introverted Sensing (Si). If Fi is the captain of the ship and Ne is the adventurous first mate, then Si is the child stowed away with a backpack full of keepsakes and candy wrappers, alternately making the journey more fun or a little more complicated.

Psychologist John Beebe called the tertiary function the “Eternal Child” or Puer Aeternus/Puella Aeterna. He described it as the “brilliant but volatile side of ourselves that is by turns the seemingly immortal Prince or Princess and the helplessly vulnerable wounded boy or girl.” In other words, this function is playful, carefree, imaginative, and even magical at times, but also extremely sensitive and easily hurt.

When it comes to INFPs, tertiary Si often shows up in nostalgic, ritual-loving, detail-rich ways. It can make you giggle at inside jokes from ten years ago, or treasure old birthday cards because of the way they smell like childhood. It loves comfort rituals: the playlist you always put on at bedtime, the soup recipe that tastes like home, the little traditions that give rhythm to life.

But like every function, Si has a double edge. When it’s underdeveloped or overburdened, it can morph into a safety net that keeps you stuck. Instead of helping you savor life, it might pull you into old regrets, painful memories, or routines that feel safe but stop you from growing. This is what typologists often call an Fi–Si loop—when INFPs over-rely on Si to retreat from the unfamiliar instead of balancing it with their natural gift for exploration and possibility.

I’ve had INFP clients tell me things like, “I know I should apply for this opportunity, but every time I think about it, I remember the last time I failed and I just freeze.” That’s Si as the wounded child, using the past as proof that the future isn’t safe.

On the flip side, when Si is integrated well, it brings grounding to all those Ne-fueled possibilities. It helps INFPs follow through, create meaningful traditions, and savor life instead of always racing toward the next “what if.”

So whether it’s the playful eternal child or the cautious homebody, tertiary Si shapes INFP life in ways that are both endearing and frustrating. And once you start noticing how it shows up, you’ll begin to see why it deserves both attention and compassion.

18 Ways Tertiary Si Shows Up for INFPs

The Playful, Whimsical Side

1. Nostalgic Storytelling
   INFPs light up when retelling quirky childhood stories, remembering details with all the nuance they can. I once worked with an INFP who could describe the exact way her grandmother’s house smelled on Christmas Eve: pine needles, sugar cookies, and wood smoke.
2. Comfort Rituals
   There’s something magical about repetition for INFPs. I’ve had clients admit they feel calmer just by sipping tea from “their mug” or listening to the same meditation every night before bed. These rituals feel like sacred touchstones that anchor them when life feels overwhelming.
3. Sentimental Hoarding
   If you’ve ever wondered why an INFP still has shoeboxes of old letters, drawings from high school, or a seashell they picked up at age twelve, this is Si at work. While someone else might see clutter, to the INFP they’re living memory banks. One INFP told me, “Throwing away my old journals feels like throwing away parts of myself.”
4. Quirky Traditions
   Tertiary Si loves to create playful personal traditions. I knew an INFP couple who declared “Taco Tuesdays” sacred—even if they were broke, even if life was falling apart, there would be tacos. These little rituals become symbolic sources of joy.
5. Childlike Wonder
   Few things light up an INFP like a familiar smell, taste, or sound. The smell of rain on hot asphalt. The opening chords of a childhood video game soundtrack. The first bite of a dish their mom used to make. When Si stirs, it brings back wonder like a time machine.
6. Playful Comparisons
   INFPs often compare present situations to past ones in funny, whimsical ways. One client joked, “When I talk to my friend it feels exactly like the time I tried to explain Pokémon to my dad and he nodded politely but understood nothing.” Si turns memory into humor and connection.
7. Detail-Loaded Anecdotes
   You’ll hear an INFP drop a random but vivid detail into conversation: “It was 3:47 p.m. in the library, and the sun hit the dust motes just right…” This is tertiary Si retrieving stored sensory snapshots with absurdly profound clarity.
8. Personalized Time Capsules
   INFPs love creating “gifts for their future selves”—memory boxes, journals, or playlists tied to specific seasons of life. Years later, opening one of these becomes a portal back to who they were.
9. Attention to Detail (When Needed)
   When an INFP cares about something, they spare no effort getting all the details right. I’ve known INFPs who thought they were ISJs simply because they were so detailed in their work; making sure every single nuance was perfect. This attention to detail is often synonymous with ISJs, but it can also be a sign of tertiary Si. The key for INFPs is that they have to care about what they’re working on. If they don’t, the details won’t matter so much. They have to know in a big picture sense why it ultimately matters.

The Vulnerable, Wounded Side

1. Over-Attachment to the Familiar
   While rituals can be grounding, they can also become shackles if INFPs aren’t careful. I heard one INFPs confess, “I know I should move apartments, but I can’t leave this one. I’ve lived here so long and I’m terrified nothing else will feel like home.”
2. Selective Amnesia
   Si doesn’t just store warm fuzzies. It can trap INFPs in a highlight reel of their mistakes. They’ll remember the time they botched a presentation in excruciating detail, but forget all the times they were praised. And believe me, that highlight reel of mistakes will keep them up at night on countless occasions.
3. Childlike Defensiveness
   Because the tertiary function is sensitive, it can feel devastating when someone mocks their quirks. A client once told me she nearly cried when a friend teased her about keeping stuffed animals on her bed.
4. Pessimistic Proof-Collecting
   Instead of seeing new opportunities, INFPs in a Si loop dig through their memory banks for reasons why trying again will fail. “I applied once and didn’t get the job—why would this time be any different?” becomes the refrain.
5. Timid Withdrawal
   When overwhelmed, Si can pull INFPs into safe little cocoons: binge-watching nostalgic shows, rereading old books, or sticking to familiar routines rather than risking something new.
6. Ruminating on Insignificant Details
   A common Si loop sign is getting stuck on something tiny. An INFP client once said, “I still cringe at how I mispronounced that word in class five years ago.” Si replays the “blooper reel” endlessly.
7. Chronic Procrastination Cloaked in Safety
   “I need to research more first” can become a lifelong stall tactic. One INFP told me she spent three years “preparing” to start a blog, stuck in the comfort of gathering info but never hitting publish.
8. Existential Comfort Blanket
   Sometimes nostalgia becomes an escape hatch. Instead of facing painful changes, an INFP might retreat into old routines or memories, convincing themselves life was better “back then.”
9. Childlike ‘King of the World’ Swings
   Because Beebe described the tertiary as mercurial, INFPs can shift from feeling on top of the world—playful, silly, carefree—to suddenly retreating, wounded, and fragile if their comfort zone is pierced. It’s the eternal child inside them, switching between joy and vulnerability in a heartbeat.

Balancing Si with Ne

For INFPs, the magic really happens when Introverted Sensing (Si) and Extraverted Intuition (Ne) learn to dance together. Think of them like two kids on a seesaw: when one sits too heavy, the other gets left dangling in the air. Too much Si, and you’re weighed down by nostalgia, routines, and fears of repeating the past. Too much Ne, and you’re floating in a whirlwind of possibilities with no grounding to help you land.

At its best, Ne is the wide-eyed explorer—always asking “What if?”—while Si is the quiet librarian who reminds us, “Here’s what worked before.” When balanced, they keep you both curious and steady, imaginative and practical.

One INFP client I worked with said, “My Ne gives me twenty ideas a day, but my Si helps me actually pick one and stick with it long enough to see results.” Another realized her Si wasn’t a burden, it was the reason her creative projects had depth. “I loooove inventing new worlds,” she told me, “But I also like to fill them with textures from my own memories, like the way my grandmother’s garden smelled in summer or the creak of my childhood stairs.”

But balance requires awareness. Here are a few ways INFPs can foster harmony between Si and Ne:

• Notice when you’re looping. If you catch yourself saying, “That won’t work because last time it didn’t”—pause. Ask Ne to weigh in: “But what if it did? What’s a new angle I haven’t tried?”
• Use Si as a foundation, not a cage. Let memories and routines steady you, but don’t let them become excuses to avoid growth.
• Feed Ne with grounded input. Instead of overwhelming yourself with infinite options, draw inspiration from your past experiences; what genuinely worked, what brought joy, what gave life meaning.
• Create rituals for exploration. For example, every Friday, you might revisit a familiar comfort (Si) and try something new (Ne). The pairing keeps you safe while stretching your horizons.

John Beebe suggested that the “eternal child” (Si, in this case) thrives when protected by its opposite, the “Trickster” (Se for INFPs), which helps it face the world with more resilience.

“Beebe believes that development of a strong Trickster, the opposite-attitude shadow sibling of the Child (in this case Se), is essential to development of the Eternal Child to bolster its otherwise virtually nonexistent defenses.” – Mark Hunziker, Depth Typology: The Guide Map to Becoming Who We Are

Adding a Dash of Se (Without Overwhelm)

John Beebe pointed out that the tertiary “eternal child” (Si, for INFPs) needs the Trickster (Se) to help balance and defend it. But Se doesn’t have to mean bungee jumping or signing up for a bodybuilding competition. For an INFP, integrating Se can be as simple as letting the world engage your senses in gentle, grounding ways. Think of it as seasoning, not the main course.

Here are a few simple, non-overwhelming ways to dip your toes into Se:

1. Savor One Sensory Experience at a Time.
   Instead of multitasking, try giving your full attention to one thing—like the texture of a ripe strawberry, the sound of rain against the window, or the warmth of your cat curled against you. Se grows when you pause to fully experience the present moment.
2. Take “Micro-Adventures.”
   Take a different route home, explore a local park you’ve never visited, or try a new café. Small changes in your environment help loosen Si’s grip without feeling like too much.
3. Create a Sensory Ritual.
   Light a candle with a scent you love before journaling. Play a song that gets you moving while you cook. Notice how different colors, sounds, or textures shift your mood. Little rituals like these give Se space without disrupting your rhythm.
4. Ground Yourself in Nature.
   Walk barefoot in grass, listen to birdsong, or notice the way sunlight filters through trees. Nature has a way of gently drawing INFPs into the present without demanding too much stimulation.
5. Move Your Body in Joyful Ways.
   You can get creative and have some fun here! Dance around your living room. Stretch while listening to music. Go swimming, roller-skating, or gardening—anything that gets your body involved in a way that feels playful rather than punishing.

Loving the Eternal Child

Tertiary Introverted Sensing may not be the headline act in your personality, but it’s one of the most endearing and important characters in your story. It’s the eternal child that gives you nostalgia, quirky rituals, and grounding comfort. It’s also the tender place that sometimes gets stuck in replaying old bloopers or clinging to safety a little too tightly.

But remember: there’s nothing “wrong” with this part of you. Every INFP I’ve coached has confessed to both the magic and the mess of their Si. They’ll talk about treasuring the smallest details or about how one bad memory convinced them not to risk trying again. These stories are proof of the childlike wonder and vulnerability that makes you human.

When you allow your Ne to dance with your Si, you get the best of both worlds: the imagination to dream and the grounding to follow through. And when you sprinkle in just a little Se—through savoring, exploring, or moving in the present—you give your Si the support it needs to grow resilient instead of retreating.

John Beebe once said the eternal child is “by turns the seemingly immortal Prince or Princess and the helplessly vulnerable wounded boy or girl.” For INFPs, learning to love both sides of that child is the real work. Let it play, let it rest, let it teach you joy. But also guide it with compassion so it doesn’t rule your life with fear.

You can find out much more about the INFP personality type in my eBook, The INFP: Understanding the Dreamer.

Want to share a story or insight from your own life? Leave a thought in the comments! We’d love to hear from you!

Other Articles You Might Enjoy: