to lose heart; to be discouraged; to be dejected; to be exhausted; to be tired out
失敗してもへこたれないでください。
Please do not lose heart even if you fail.
連日の残業続きですっかりへこたれた。
I was completely worn out from working overtime day after day.
彼は失敗が続いてへこたれている。
He is discouraged by the string of failures.