I hate not being able to come to a solution. Does life have an equation?! Of course not. If it does, it is unsolvable. Or how about a chaotic system?
Frequently I find myself rewinding to some point in the past and going "What if I had done that?". Regret? Sometimes. It depends on my frame of mind.
I have realized that Physics and Math... anything scientific and (mostly) deterministic is a safe haven for me - a retreat - a defense mechanism even. Life is not deterministic... and sometimes you know nothing about something.