The term "forgettable contraception" has received less attention in family planning than has "long-acting reversible contraception." Defined here as a method requiring attention no more often than every 3 years, forgettable contraception includes sterilization (female or male), intrauterine devices, and implants. Five principal factors determine contraceptive effectiveness: efficacy, compliance, continuation, fecundity, and the timing of coitus. Of these, compliance and continuation dominate; the key determinants of contraceptive effectiveness are human, not pharmacological. Human nature undermines methods with high theoretical efficacy, such as oral contraceptives and injectable contraceptives. By obviating the need to think about contraception for long intervals, forgettable contraception can help overcome our human fallibility. As a result, all forgettable contraception methods provide first-tier effectiveness (</=2 pregnancies per 100 women per year) in typical use. Stated alternatively, the only class of contraceptives today with exclusively first-tier effectiveness is the one that can be started -- and then forgotten for years.