Lái ér bù wǎng, fēilǐ yě.*

來而不往非禮也。

Lit Taking and not giving is not polite.

Fig It's impolite not to reciprocate a gift.

Note [Cf. Lǐjì: Qū Lǐ Shàng; now sometimes used ironically to justify striking back, like “One good turn deserves another.”]

Topics Book of Rites COURTESY FIGHTING GIFTS IRONY Lǐjì Qū Lǐ Shàng RECIPROCITY