Think of any relationship that you have. Why do you like or love that person? Why do they like or love you in return? Is it because they do things for you that you enjoy? Do they listen when you're down, provide a shoulder to cry on or surprise with a simple kind gesture when you really need it? Or, do you love them because they just make you feel good when you are around them? Does this person like or love you because you do something similar for them?
The answer is... probably. Most human relationships are based on reciprocity, meaning that people like you for what you can do for them or what value you add to their lives and you like people for what they can do for you or what value they add to your life. Before you start shaking your head, saying that you're different, and you're not just out to get things from people or gain something by having a relationship, just think about it for a moment. If you do, you'll realize that it is true. Family, friends, boyfriend/girlfriend, teachers, role models... whatever relationship you have. If you serve no purpose to someone, do they still love you? If someone serves no purpose to you, do you still want them around? Chances are, the answer to both questions is no.
But what if there was one relationship that was not like this? What if there was a relationship in which you knew that you had absolutely nothing to offer that was really needed, but you were still loved in return?