I think a lot of relationships don't last because you meet someone, they make you laugh, you go out and have a good time, you can talk to them, and you feel a genuine connection.
Then, down the road, you realize this person doesn't have the best communication skills, they aren't accountable, they aren't respectful of your relationship, & they have issues from their past that affect their present.
The difference is that the first set of attributes are things you seek in a friendship, the second set are things you seek in a long-term relationship.
A lot of us have created lives with people we should've just been cool with.. What do you think?