I have so many.
I was very smart at school and my family encouraged me to go into a scientific field because it would make me employable. I didn't really gel with my degree subject and just felt really guilty about not loving it, rather than being pragmatic and finding something else.
I got into a relationship with a manipulative, abusive arsehole when I was 20-ish and stayed with him for 6 years because I genuinely thought he was the best person I had ever met.
I made unwise career decisions because of that relationship. I was actually quite successful and well paid in a technical role, but found it stressful and unfulfilling.
I quit to retrain to work in the NHS. I was really proud to have got onto a very competitive paid training program, but now I'm close to qualifying and there are no jobs (like 2 in the whole of Scotland) because of big service cuts and I'm really scared. And my CV looks really weird because I moved field and started from scratch.
I put off having children for a few years because of the career change and the abusive relationship. Now I have a 2yo DS but I'm over 35, just had a missed miscarriage and am scared I left it too late to give him a sibling.
I don't know what I've learned from all this. On the one hand, I had a far from ideal start in life, have done lots of really interesting things, got myself out of shitty situations and made a good success of lots of things. I'm married to a good man, I have a child and I'm nearly in the career I wanted. But I also feel like I played my hand as hard as I could and it still wasn't quite enough.