Among Science Daily's 10 things men need to know about women, one is that women are easily turned off. For a woman to have an orgasm, all must be right in her brain. Anger, stress, or physical discomfort (like cold feet) can keep a woman who wants to be in the mood on the sidelines.
Since most of a woman's brain shuts off when orgasming (except for the cerebellum, which controls movement), it makes sense she'd need a clear head to get there.
The best advice? Researchers suggest men focus on 24 hours of emotional and physical foreplay before sex. Now that is news he can use!