幸福如饮水冷暖自知
[xìng fú rú yĭn shuĭ lĕng nuăn zì zhī]
'Happiness Is Like Drinking Water, Warmth or Coldness Felt By Oneself Alone' indicates that true happiness (or its absence) is a personal experience that only oneself truly understands; it's deeply private and unique to each individual.