From the essay of the same title from the book of the same title by Harry G. Frankfurt:
“What makes it more suitable, then, for a person to make one object rather than another important to himself? It seems that it must be the fact that it is possible for him to care about the one and not about the other, or to care about the one in a way which is more important to him than the way in which it is possible for him to care about the other. When a person makes something important to himself, accordingly, the situation resembles an instance of divine agape at least in a certain respect. The person does not care about the object because its worthiness commands that he do so. On the other hand, the worthiness of the activity of caring commands that he choose an object which he will be able to care about.”
Common Sense 