Relationships falling apart

What do relationships crash so soon?

A friend once said she would love to have a guy who would love and cherish her, respect her opinion,listen to her.

Another friend say he would love to have a lady who would always say yes to his wishes,one who would never question his Authority, one who would be at his beck and call.

So, here comes the question.........what makes a relationship fail?
I can't help but wonder why relationships that looked like they were made in heaven crash before bingo is said, People who made friends and family members believe they were really crazy in love and told everyone who cared to listen they want to spend their lives together forever not matter what happens. Eventually they are married ironically they wont even last for a year,sometimes even 6months after the marriage comes down crashing.

These keeps me soliloquizing......."what ever happened to happily ever after".
I think immediately a relatioship starts, priorities should be set, the fire in your first days of the relationship should be kept burning, There's this word called Tolerance it should be applied to keep a relationship going.
Concluding, we should try not to have our own way at all times(selfishness), it's the nail that that punctures the tire of any relationship.