I definitely had a bit of a lightbulb moment with one thread I posted a few years back.
DD (12 at the time) was saying they were depressed and I was wondering whether they really were, or just a bit sad as I cried a lot and was very sensitive at that age but I don't believe I was ever depressed because I still maintained an optimism that the next day might be better, unlike the endlessness of negative feeling that friends/family members living with depression have described. So I asked MN and of course there was the share of people accusing me of being an unfeeling witch who didn't believe my child (I was just saying I wasn't sure and my intention was to get her help regardless, and I did and it helped) and some also fairly harsh, but totally fair, I thought, points about not projecting my past self on to my child. I've kept that one with me since, and suggested it might be an issue to other people when I've realised they were doing what I was doing and assuming their child was like them.