百毒不侵的人都曾无药可救刀枪不入的人都曾遍体鳞伤
[băi dú bù qīn de rén dōu céng wú yào kĕ jiù dāo qiāng bù rù de rén dōu céng biàn tĭ lín shāng]
A person immune to all poisons was once beyond saving; an invincible person was once riddled with wounds. The expression metaphorically describes someone now seemingly impervious but who has had intense suffering in their past.