1. The guy is gay
2. The guy does not find you attractive
3. The guy already has a woman much higher than you on the ladder
Even Nietzsche knew this. Most guys know this intuitively. Most girls doubt. I have a challenge for all of you girls who still doubt. Pick a guy who does not meet any of the criterion on the above list that you think is your friend. Then ask yourself this question: If you were both alone at his place one night, and you excused yourself to the bathroom and came out naked and asked him to have sex with you would he:
1. Tell you he doesn't want to risk the beautiful friendship you have created with messy physical entanglements.