When I say - what we want from the one we have a relation with, I sound somewhat selfish. Isn't it a common characteristic of us that we "want" something from our relations? Selfishness is a common trait that we all share. All. The difference is quantity and quality of selfishness. This is not to say there are only selfish people on the planet, in fact, the word itself is little too strong.
There is this phrase "returning favour" which in itself is based on some sort of selfish attitude. Just look at the structure of a relationship and you will find there is always a kind of reciprocal element in most of them. The relations that are mutual in nature are also in some ways dependent on this "reciprocal" element. Consider a mother-child relationship, which I think is one of the strongest relations we have. A mother cares for her child no matter what the child does. Some call it divine and others call it natural (essentially both lead to same thing). Even if the relation is divine, their are certain expectations the two have from one another. A child "wants" his/her mother to feed him/her, which if not done may change the equation of their relation. What did you say? this is not selfishness? well, I agree. This is not the kind of selfishness we generally know, but it certainly is one of its kind.
My post is not about proving we all are selfish people. Not at all. What I want to say is there are some expectations from relations and this understanding is very helpful in managing our relations. Expectations are there even if there appear to be no relation at all. For example, my friend Jaunesk posted "Questions are The Answers" on his blog, in which he highlights how a salesman needs to be a good listener. I put that in this way - the relationship of a sales person and his potential customer is dependent on how good the sales person fulfils what the customer "wants" and the better listener the sales person is, the better he satisfies the requirement of this relationship.
If we focus on what the other person in our relationship wants, we are not serving the God of Selfishness but just managing our relation. They say expectations are the root of our sorrows. They are right. But, the fact is we just can't be machines and if we are humans, we got to have some expectations. So do the ones who have a relationship with us. Like anything else, too much of it can be as bad as the lack of it. It has to be balanced - both the expectations as well as our desire to fulfil them.