Um, a lot of them.
As humans, we rely on heuristics (simply put, using experiences to problem-solve) a bit too much. In the majority of our daily lives, this is okay. But not when it comes to sex. Just because someone looks like they don't have a disease doesn't mean they don't. And just because you assume your partner is on the pill doesn't mean they are (can you say 'pregnancy scare'?). Clinical sexologist Dr. Lindsey Doe has a few things to tell you on the collision of sex and heuristics, so listen up.