裏切る

To break faith with someone or something, often by acting against their trust, loyalty, or expectations. This can involve actively harming a person or cause by revealing secrets or changing allegiance, similar to `betray`, `double-cross`, or `backstab`. It can also be used in a broader sense to describe a situation where something (e.g., one's body, luck, or an object) fails to meet an expected standard or function, thereby disappointing or letting one down. The Japanese term often carries a nuanced sense of a violated bond or implicit agreement, whether personal or abstract, which can be less direct than the strong malice often associated with English verbs like 'betray'.

• 彼は親友を裏切って秘密を暴露した。 — He betrayed his best friend and exposed the secret.
• 彼女はどんなことがあっても私たちを裏切らないと信じている。 — I believe she would never betray us no matter what happens.
• ファンたちの期待を裏切らないように頑張ります。 — I will do my best not to disappoint the fans' expectations (literally: not to betray the fans' expectations).
• 長年の練習にもかかわらず、本番で体が裏切った。 — Despite years of practice, my body betrayed me during the actual performance.
• 天気予報が我々のピクニックの計画を裏切った。 — The weather forecast betrayed our picnic plans (meaning, it was wrong and ruined the plans).