Expectations - II

Why do we have expectations? Why, if we do something for others, we expect them to return it in some way? Even when we say that we are doing it without expecting a return, our sub conscious knows that we still want them to reciprocate in some way. Don't we? Expectation, once you start having them is a vicious circle. You do, you want them to do, then they want you to do.....n it goes on. Why can't we just do good to others and forget about it? Why, Why, Why???