According to the "Ladder theory" (you can google it if you want to read the whole theory) men don't separate between "friends" and "more than friends"/"possible sexual partners" when it comes to women. Whereas women instantly decide whether or not a guy is "just a friend" or "more than friend" and once she has made up her mind it is very difficult for the guy to jump from the friends ladder to the more-than-friends-ladder.
Which would explain why it seems to be more difficult for a man to be "just friends" with a woman then it is for a woman to be "just friends" with a man (because men don't separate between different friends and 'more than friends').
Is there truth behind this?