moral fibre

moral fibre (ability/guality of having the courage and the inner strength to do what you believe to be right in difficult situations ) — сила духа, сила характера; мужество

Example 1: He lacked the moral fibre to win. — Ему не хватило силы духа для победы.

Example 2: He showed great moral fibre in speaking out against the injustice even though he knew that he would lose his job.

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(In American English the correct spelling is 'fiber'.)