A key to a satisfactory life for many people is a long and happy marriage. Few people, single or married, are completely satisfied with their lives. If there is any spark of interest in someone of the opposite sex, a determined campaign by that other person can intensify the relationship. The usual strategy is to promise or freely offer something that the other person does not already have. The price can be high, however, and the rewards few. A happy marriage requires the full-time commitment of both partners.