history
From Zhuangzi (《庄子·山木》): 且君子之交淡若水，小人之交甘若醴 - 'A gentleman's friendship is plain as water, a petty person's is sweet as wine.' The moral: friendships based on shared values outlast those based on favors and flattery.
usage
Often contrasted with 小人之交甘若醴 in formal writing. Used to decline gift exchange, praise a long-standing low-key friendship, or describe unostentatious social relations.
