expression, godan verb (-ru)
prepare for the worst; steel oneself; accept one's fate
Idiomatic expression meaning to mentally prepare for a difficult or unavoidable outcome, often with a sense of resolve or resignation. Used when facing a challenge, risk, or inevitable hardship.
試験に落ちるかもしれないが、もう腹をくくった。
I might fail the exam, but I've already prepared myself for the worst.
彼は腹をくくって、会社を辞める決心をした。
He steeled himself and made up his mind to quit the company.