百炼钢也成绕指柔
[băi liàn gāng yĕ chéng răo zhĭ róu]
Based on an ancient Chinese idiom 'After repeated refining even iron becomes soft like silk thread at one’s fingertips.' It describes someone who is tough yet also has a softer side. Tough and hard things are not always rigid; they can also be tender and considerate after being repeatedly polished.