There is this saying that being best friends doesn't necessarily mean you'll both be best couples.. This statement as little as it may seem, has influenced so many friendships and pushed a lot of people into marriages they had never enjoyed. 
I've once been told by a female friend that "we are cool as friends and may not really do well in a relationship". All that came through my mind was maybe I had made myself too available for the lady making her not want a relationship. This prompted my curiosity into searching around for successful marriages and whether or not good friendship had existed before their relationships.
The outcome was remarkably shocking because a lot of people I met were of the a totally contrary opinion from what the saying above depicts. Majority that had their best friends as their spouse had the most relaxed environment as home, no pressure whatsoever on what surprise will this my wife/husband bring up today. For majority of their actions, they could anticipate. Yes, they'll have arguments but they make-up in the most romantic way.
I made a conclusion that Friendship is sweet especially when both parties have gone through every hurdle during friendship unchartered. When these friends decides to step up into a relationship it becomes sweeter, and if they eventually get married it could become the sweetest thing ever to happen to the couples.