I feel this way too and I'm not entirely sure what causes it (or where it stems from, for that matter).

My family life has gone well the majority of the time, though I'm an only child --- so even from a young age I was more independent/mature/stoic.

It may stem from the fact that I'm a taller/larger person, always have been. It was tough when I was a kid, especially since I was emotionally sensitive. Because I'm bigger, people have seemingly found me threatening even while carrying on a friendly conversation. That impression wears off when people get to know me, of course, but it's something I've struggled with accepting.

Sensitivity in itself caused an entirely different set of problems, because as soon as they saw me cry? Bam. I got crap from all sides. Maybe that's why I don't trust people these days...even friendships back when I was a kid changed once I "got emotional". So I became more reserved and insular as I got older, showing emotion only when I truly needed to. Even the school bus driver once called me out on a "guilty conscience". I forgot nothing.

I don't know why I'm so quick to jump to being at fault even though it may not be mine. It's also that same way at work, as I'm such a stickler for detail that I go back and say "I should've done that before it became a problem". So in some respect I bear some share of the responsibility, even though rationally I know I am not entirely to blame.

Anyway to tie this all up, I'm really not sure where it comes from. It could be a different cause for different people, or maybe even be equally learned and inherent. It's something I've tried to answer for a long time now. And when it happens, it's almost instinctive.

When I get this way, I remember a line from "Town Called Malice" by The Jam: "stop apologizing for the things you've never done". But for me, it's not that easy. It's almost as if apologizing is instinctive for me. Best I can do is shift that impulse from the emotional to the rational side of my brain.