There are countless of things that can go wrong with the person you're trying to build a relationship with.
I would have to say that lack of chemistry is my biggest dealbreaker because it's hard to fake connection that never existed to begin with. If it's there, great, if not then that's too bad. Life is too short to be pining over someone who isn't compatible with you.

If I were physically at my prime I would take up lacrosse because it's action-packed and filled with excitement. If I'm having a bad day and need to release my anger, lacrosse would be the go-to sport because being wild and crazy is totally acceptable.