百毒不侵的人曾都无可救药刀枪不入的人曾都遍体鳞伤
[băi dú bù qīn de rén céng dōu wú kĕ jiù yào dāo qiāng bù rù de rén céng dōu biàn tĭ lín shāng]
The one who's now resistant to all harm was once helplessly vulnerable; the impenetrable person was once heavily scarred. It reflects on the process of growing emotionally stronger by experiencing and overcoming pain and hardships.