約束を忘れてはいけない。

promise; agreement; arrangement; one's word; contract; pact; appointment; engagement; date; convention; rule; destiny; fate

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)

if ... then; when; and; why don't you...?; the more (one does something); because; since