1. Character Flaws - They are always there. They cant be avoided. She's scared or he's selfish. He's a player or she's cynical.
2. History - He's already broken her heart. He's already destroyed her hope. Or maybe she made a bad choice.
3. She's already decided not to have him - for whatever reason she decided not to go there perhaps because of a characteristic he shares with an ex.
4. Business Nemesis - they work against each other but they work close together.
5. Intimacy Issues - his or hers, we've all got issues.
6. They believe they can't be loved - a terrible mistake in the past or they've been blamed for something that wasn't there fault.
7. Friendship - they don't want to lose each other.
8. Secrets - keeping secrets makes having a relationship impossible.
9. Only sex - friends with benefits, an agreement, he's an escort, she''s a prostitute - falling in love is against the rules.
10. It wasn't supposed to be real - it was meant to be pretend.
11. Forbidden - their families hate each other or maybe their friends.
12. Money - he's rich. she's not. That always wins.
13. Other relationships - he's married but they aren't together any more.
14. She thinks she loves someone else.
15. Time Limits
16. Sacrifices they aren't willing to make - what if they have to give up their dream.
17. He makes her unsafe - he's a spy or something.
18. He's the beast like beauty and the beast.
19. Disguised - she's a reporter pretending to be someone else.
20. Family complications
21. Reputation - he's a player and she's a good girl and her parents won't like it.
22. Freedom - she doesn't want to settle down.
23. He's a workaholic.
24. He doesn't want to see her that way because she's his friend's kid sister.
25. She's sick. He might die.