When you start liking someone, do you ever try to find out the reason behind: Why you like that person? No, you don't. Because, liking is the manifestation of a unique shade of your emotional existence and it doesn't follow a definite criteria.
Well, over a period of time, through mutual interactions, you may find that person to be quite different than what you initially thought about. Still, in all probability, you continue with your liking, because, frankly speaking, you don't know why you do so.
The degree of liking or emotional attachment that you develop with that person is mostly determined by your initial assessment of his/her personality and, in most of the cases, it doesn't undergo any major change even if things go wrong in course of time.