According to a new study in the British Journal of Psychology, while guys do value altruism in a long-term partner, they found it slightly off-putting when they were looking for short-term relationships. "This could be because men fear that altruistic women will be too interested in other things and not enough in them," postulates Dr David Lewis, a member of the British Psychological Society and author of Loving and Loathing: the Enigma of Personal Attraction. "Men are very egotistical and see themselves as the sun in their own world." Which is to say men don't want to bask; they want to shine--and be worshipped. It's more that men like a challenge--and any woman who is seen as particularly kind or selfless doesn't come off as hard-to-get. But when a guy falls in love, his game-playing mentality falls away (and he can appreciate a woman who's sweet).