to fire after the horse has bolted (idiom); to act too late to be effective
Definitions (粵典–words.hk)
動詞、俚語
喺件事搞掂咗之後先評論，扮有先見之明 (literally: to let of firecrackers behind the horse) to begin to make comments and criticise after something is already supposed to have been settled
動詞、俚語
唔願意接受對自己不利嘅結果 to refuse to accept the outcome or result, to be a bad loser