“痛苦的经验”可以翻译为 "painful experience" 或 "bitter experience"。
"Painful experience" 强调经验带来的身心痛苦感，例如：The accident was a painful experience that he would never forget.（那次事故是他永远无法忘怀的痛苦经历。）
"Bitter experience" 更侧重于经历的艰难、令人不快或带有遗憾色彩，例如：Her bitter experience taught her to be more cautious.（她那段痛苦的经历让她学会了更加谨慎。）
根据语境选择合适的表达即可。