For me a lot of the things that upset me about the past are that I didn't make friends when I feel I should have at school, at university etc. I hung put with people but they made no effort to see me. It used to make me feel like they didn't like me or at least didn't like me enough to bother with me which made me feel like I must have a unappealing personality and made me really depressed as a result.
Now I just see it as it was only because of my social anxiety and nothing else. It wasnt because I have a bad personality in any way. I was too anxious to just relax and be myself and so I didn't talk enough so people didn't get to know me well and may have wrongly thought I was boring, probably didnt give off a particularly good vibe, and probably came across as having little confidence which is unappealing. BUT this is all because of having social anxiety. This realization makes me feel so much better about myself AND hopeful for the future when my social anxiety is no longer a problem.