Vault 11 was part of an experiment to determine inhabitants' willingness to sacrifice one individual each year to ensure the safety of the remaining population. Its overseer was told that the vault mainframe would kill everyone within if the sacrifice was not made. When he informed the dwellers of this, they elected him as the first sacrifice. Since then, overseer and sacrifice became synonymous. Each year, the dwellers chose a sacrifice via the overseer election, to be killed at the end of their term.