The bodhisattva vow is taken publicly, in ceremony, and it commits the taker to something that cannot be finished. Beings are numberless and the vow is to free all of them; the classical formulations pile the impossibilities up deliberately — delusions inexhaustible, dharma gates boundless. The tradition's explanation is that a completable goal would let you finish and stop, and any goal you could finish would be a goal about yourself. In practice the vow reorganises the ordinary business of a life around other people rather than adding a task to it, and teachers advise taking it long before you feel qualified, since feeling qualified is not one of the conditions.