forgetfulness; leaving things unfinished
Describes a person who starts things but doesn't finish them, or who forgets things easily. Often used in a mildly critical or teasing way.
He's a forgetful person who never finishes his work.
That person is forgetful, so they might have forgotten the promise.
Compound of 尻 (しり, 'buttocks, end') and 抜け (ぬけ, 'missing, omission'). Literally 'missing the end', referring to something that lacks a conclusion or a person who doesn't follow through.