In a sense, searching for a mate is not so different from hunting for a job. Jobs, like prospective partners, have their strengths and weaknesses, which makes finding the right one a matter of complicated trade-offs. Such exchanges are different from other transactions, in that both parties must be enthusiastic about the match for it to happen. A supermarket, in contrast, does not particularly care whose wallet it is draining, nor does the power company agonize about whether a customer is worthy of its watts.