When a child at a party does not have any cake, then have a slice, their utility goes up! However, when they have another slice of cake, that second, and third, and forth slice of cake does provide that same level of utility as the first. The incremental, the marginal, amount of utility starts to decrease. Classical economic theory assumes that marginal utility decreases, and that consumers seek to maximize their total utility by choosing the next best consumption such that it has the highest level of marginal utility