Back to school
I chose the wrong major. I started out in a liberal arts field and was on my way to changing my major to a science because I thought I'd have more opportunities.
I was taking the prerequisites for one of the science programs one semester and they were difficult, but I studied a lot and did well.
That semester I was also taking a class I had chosen almost randomly out of the list of courses that satisfied a humanities requirement. That class was also difficult and I had no interest in it, but I wanted to stay in it and impress my professor because he was hot.
I ended up dropping my science prerequisite courses because I became too stressed to handle the workload of both the humanities course and science courses at the same time. I could have and should have dropped the humanities course and taken an easier one the next semester, but I dropped the science courses and returned to my original liberal arts major.
But that was all before the recession hit. I've graduated and now I find myself in an economy where my major isn't going to get me a good job. I will never forgive myself for ruining my chances because I was stupid enough to think that a hot professor might f*** me if I seemed smart enough, and that that f*** would be worth my future.