People of Reddit, what are your most interesting, amusing (?), and/or heartbreaking stories of chances that you did or didn't take with other people?

This question was inspired a few days ago, when I met a guy at the beach and spent a really nice night walking and chatting. I've never instantly hit it off with someone so well. He sat with me through the sunset, walked me home, gave me his number when I left... and basically, I decided not to use it.

To be blunt, I've rejected a lot of advances in a lot of different situations, for a lot of different reasons. In this case, I ended up feeling that some things are just better left alone; it's a memory I can look back on to remind myself that there are good people out there, who will find you even if you're not looking. That said, though, there's always that little question of whether or not "Jon" could have been a big part of my life, if I'd taken a chance with him.

So, Reddit, what ridiculous or beautiful encounters have embraced or avoided, and why did you act the way you did?