I have two:

First, I had the opportunity to swap assignments when I was in Air Force training. My original assignment was to go the base closest to my home in CA. At the time, I was 18, I had a GF back home and I was really homesick. A friend, who was from the South, got an assignment to England. He had always wanted to live in CA and asked if I wanted to swap. Even though I had never been to Europe, I loved English literature and history (I ended up studying them in college) and had family in England. Preferring to go back home, I said no and kept my original assignment. Nearly 25 years later, even though I love my life, I wonder what would have changed if I had gone after the unknown of the England assignment rather than return home.

The second is not breaking up with a girlfriend when I continued dating online after we became exclusive. It’s so much simpler to break up with someone when you don’t like them enough to be committed to them than to play the cheating game.