It’s cool seeing that something I did in the game is something that only a small number of players did.

This is the most enjoyable part of achievements for me too.

I had that fun moment in Caves of Qud when I was going through a quest in Bey Lah, an isolated village of deertaurs who are ruled by an authoritarian shithead who is very suspicious of outsiders. I was given a quest to solve a mystery and I ended up blaming outsiders, genuinely thinking that this was what happened. Then, this achievement popped up:

And I realized I just helped the fucking leader of all people there! I mean, I'd realize it anyway even without the achievement but it wouldn't be as big of a jump from "yay I completed the quest" to "I fucked up so bad". It'd be less funny.