seal (one's) fate
To solidify or confirm that a particular, usually unpleasant, thing will happen. If you fail this exam, it will seal your fate and make your GPA low enough to qualify for expulsion.
seal someone's fate
Fig. to determine finally the fate of someone. His lying and cheating sealed his fate. He was convicted and sent to prison.
seal one's fate
Decide what will become of one, as in The letter of rejection sealed his fate; he'd have to apply to other medical schools. This term employs seal in the sense of "permanently fix or fasten something," a usage dating from the mid-1600s.
seal someone's fate
COMMON If something seals the fate of a person or thing, it makes it certain that something unpleasant will happen to them. The plan removes power from the government, sealing the fate of the unpopular Prime Minister. It was his decision to walk that night, rather than taking a taxi, that sealed his fate.
seal someone's fate
make it inevitable that something unpleasant will happen to someone.