黑咖啡不加糖的滋味是苦纯牛奶加了糖的滋味是甜
[hēi kā fēi bù jiā táng de zī wèi shì kŭ chún niú năi jiā le táng de zī wèi shì tián]
Describing coffee without sugar tastes bitter, and milk with sugar tastes sweet. The phrase juxtaposes two contrasting tastes, possibly referring to life experiences – hardships vs sweetness.