Men are full of surprises, and bedroom behavior is no exception. To get to the bottom of things, it took one of their own -- and a psychologist at that -- George Weinberg, author of Why Men Won't Commit: Getting What You Both Want Without Playing Games, who studies male behavior in romantic relationships. While we can't explain all male behavior, here are five sex secrets that may help you understand -- and get even closer to -- your guy.

1. He's afraid he'll let you down -- literally. Men feel tremendous pressure to perform sexually. "In the past, men weren't evaluating their sexual performance because women weren't supposed to judge them," says Weinberg. But women aren't waiting for marriage to have sex anymore, and that means they have more experience in the bedroom. Sexually satisfied role models, like Madonna and the Sex and the City sirens, encourage women to be open about their sexual desires and complaints. Suddenly, the pressure to perform is on, and he can't help but feel like he has to please you. Even though you might forgive him for a few poor performances, he has a hard time forgiving himself.
Warning: If your man has a recurring problem getting aroused or maintaining his erection, he may start to blame you to protect his ego.
What you can do: Dr. Weinberg suggests something simple. Just relax and try to enjoy sex, which will help to alleviate some of the pressure. In other words, don't take it personally or, worse, insult him. And never point and laugh!

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2. Men need validation to get their groove on. Sex is a source of power, and it gives proof that one is masculine. "To a man, having sex means that he can move a woman, that he's an athlete, a provider and a lover," says Weinberg. Basically, your guy wants to be a superhero, and he certainly wants you to see him in that light. When he satisfies you sexually, he feels like Superman. If you're enjoying yourself, let him know that Lois Lane is happy, adds Weinberg.
Warning: No encouragement means no mojo.
What you can do: It's simple. Say, "That feels good," or let out a moan or heavy breath when you feel like it. A good rule of thumb: Don't fake it but don't fight it.