[saying]
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⇒ по matter how you try to change s.o., win s.o. over, his true nature, feelings, habits etc will surface:
- ≈ a leopard cannot change its spots;
- once a wolf always a wolf;
- nature is stronger than nurture;
- what is bred in the bone will come out in the flesh.
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.