When it comes to knowledge, I'm torn. My librarian side wants everyone to read more, but my spiritual side believes moderation is key, and that too much of a good thing is just as unhealthy as nothing at all.
The expression simply means take your time to get to know someone well -- male or female -- so they can earn your trust instead of giving it away. It's about protecting yourself from potential disappointment.
Years ago I was giving advice on a TV show about cheating and lying partners. When I got to the last woman, she began to vehemently defend her jerk. "You don't understand. If it wasn't for the lying and cheating he'd be perfect."