When it comes to the subject, I can think of one thing and it wasn't long ago. Namely when I dropped out of my studies. Back then I had a goal that I wanted to pursue. I took Sam Flynn from the film TRON: Legacy as a model. I don't know if the title says something to everyone, but if not, be sure to check it out.
http://latenightstreaming.com/de-de/film/tron-legacy
Sounds a little funny but it really is. I already knew that when the film came out and I was a teenager.
Having a goal that you want to achieve and then failing just before the goal is really bitter. I'm lucky enough to have repented in time and have the chance to move on. So to everyone who regrets something. It is MOST possible to change the situation or, if it's too late, to be happy with it anyway.