The first thing comes to mind reading the question is failing first year of university, I developed because of it chronic stress, IBS and eye problems. but if I were to relive the same year with the mindset I have today, it would be of no effect

I believe the lowest part of someone's life is more a reflection of their psychological strength than of the situation itself. That's why I sympathize with people going through hard times, even if the thing causing them to feel down seems trivial to me.