INFJs are as varied in individual terms as any other type.
I wouldn't accept being an INFJ for a long time, so this trend--if it exists--for so many typing themselves as one? I don't get it.
On the INTJf where I was an active member for eight years most people were mistyped as that, which makes more sense as it was started and peopled by INTJs, almost exclusively, for the longest time--still the majority are INTJs, but here on PerC, if there is any over-represented type it would be INFPs (maybe I hang out too much in the game threads in that sub-forum and don't see the INFJs all over the place).
I do know at least one INFP mistyped herself as INFJ after saying 'she cannot see her "Fi" as though having the equivalent of a Johari mirror blind spot naturally, or by default, "makes her an INFJ" whose aux is Fe. (Shakes head, internally.)
The one obvious reason for mistyping I haven't seen noted is an obvious one to my mind: Neurotic self-idealized type being mistaken--unconsciously--for the real deal as it got ingrained early, e.g. parents pushed tasks, lauded attributes, rewarded behaviors in align with a particular type (don't need to know anything about MBTI for this to happen) and voila, got a person who has come to prefer and believe he or she is some other type than what he or she is, 'and' to discover that person's real type would take recognizing the idealization going on; want to change; do the work; go through the vulnerability of coming down to earth and so on:
Most aren't going to do this regardless of type they put in front of their real--and possibly amorphous--self.
It's not just INFJs.
I've seen so many assert being "risk-taking ISTPs" when they're INFPs, or some who come on strong and shooting off their mouths in a circle like guns blazing, have ESFJ as their type, totally obvious, wrong, and once the person comes clean: ISFJ there, calm sets in (not too neurotic person in that case--actual guy over on INTJf).
Factoring in medication changes comes to mind.
I have an ISFP relative brought up in a chaotic, violent, drunken environment laid low, went to church, quietly compliant until she hit 30 and busted loose: Stopped attending church; had an affair, got tattoos, began hanging out with a narcissistic sister and doing all sorts of out-of-character shit, then got on Paxil and she's a real mess: Thought it would be a great idea to demonstrate how effective her taser would be on the boss's wife, no kidding--almost got her fired.
She's become a pathological liar and more.
Is she still an ISFP?
Yes, I believe she is, but the early childhood trauma--she couldn't repress it any longer, and when it surfaced, her real feelings about it--a lot of rage, bam! she came across loony tunes, MBTI aside.
I am grateful for the many who pointed out the volunteering and leadership and social aspect (though I do need a lot of alone time, it isn't--to my mind, because of being an INFJ; it was my huge, overbearing, take and not give family members and a whole lot worse, early).
I used the only blog space I had before the one I keep stuff in here for another purpose, connected to foster care fall-out: I never knew when I would be removed and my things left behind, or when an older sister or my mother would literally break open my childhood 'keyed' journal and read--then share--the juvenile entries, so I copy/paste posts into the blog spot here as I did on INTJf.
Otherwise, I've never blogged; never felt the need as I published whatever I wanted to share, and "journal entries" generally made me feel worse, not better as they were reflections of the chaos, and did not bring order to it as my published writing did.
And I don't feel 'misunderstood.'
I don't think I ever thought, let alone said that.
Sure, but in my family of mostly self-centered, anti-intellectual ESFPs, that's hardly surprising.
Glad I married an ESFP who likes my being smart and doesn't care much about MBTI beyond how my learning the nuts-n-bolts improved our marriage--topic for a thread I've already contributed to, and may go back for another pass if I got more to say.