Loneliness does not come from having no people about one,
but from being unable to communicate the things that
seem important to oneself, or from holding certain views
which others find inadmissible.
                              - Carl Jung

*

I didn't realize how many people I knew in person who were the same type as me for a long time, because I was looking for something "else" that would let me know how alike I was to other INFJs, some "sign" that would provide a flash of recognition, that would help me identify a kindred spirit.

That rarely happened.  And here's the ironic thing:  I recently figured out that my financial planner and my last realtor had INFJ preferences.  They were under my nose all along!  How come I didn't "know"?

It's not just me.  I bet you could have 20 INFJs in a group, and they wouldn't realize they were all INFJs....  AND even if they did, they wouldn't feel they're much "like" the others.  We feel different, even when we are surrounded by other people who are INFJs and similar to us in every way (age, race, education, income).  We would find a way to feel different.  Most INFJs perpetually live with this sensation of being isolated, feeling different from the pack.  Even when we aren't isolated, we tend to FEEL isolated, despite all evidence to the contrary. 

I have some thoughts about that -- about why this illusion of rarity haunts us.  (Because I think this sense of "rarity" springs from something more elemental than unverified statistics.)  

I suspect it's because we're so doggone complex, we feel nobody's like us.  Because our inner worlds are so rich, we don't suppose anyone shares our experience. (And truthfully, they don't.  How can they?)  And being "like" others is usually about shared experience.  

In turn, "shared experience" is usually about using extraverted processes -- which is not our primary thrust.  It's not what we do best.  I don't know about you, but I'm not much of a "reacher-outer."  Just posting online sometimes is about all the socializing I can manifest.  I like to feel "connected," but if I have to make a lot of effort to maintain a relationship, I'll just let it go.

On that note, if you look at INFJ online communities, they aren't all that social either.  Unless there is some conflict or drama that calls INFJs out of their shell to advise, "fix," or use their talent for diplomacy, they may not have anything they feel like talking about.  When INFJs *do* connect, it tends to be around shared causes.  At least that way we're guaranteed of having something in common.

So the upshot is that INFJs may not be all that rare in reality, but can't shake off that sensation of uniqueness, even when surrounded with others of the identical pattern.  And that's a logical outcome of having INFJ preferences.