Guys, what is the biggest mistake you made in your life

[greyblob]

not visiting my grandfather when he was in the hospital even when he asked to see me. he left soon after. also, not going to an old friend's funeral.

 

[CharlesEBrown]

Something that you regret, something you will change the first second you get a time machine

I don't recall anything like that, though my wife tells me my memory is going (fortunately, she remembers almost everything I should regret, even most of the stuff before we met...).
I would not change anything in my own past. I would, however, love to be able to view the alternate timelines and see how my life turned out if I made different choices at various points, mostly concerning the girls, women, one guy and one I still don't know what it was (probably female but only about 60% certain) that I have been attracted to over the decades...