Wei Wu Wei

Why aren't you happy? It's because ninety-nine percent of everything you do, and think, and say, is for yourself - and there isn't one.

Source: Ask the Awakened: The Negative Way, Wei Wu Wei, 1963

This is Wei Wu Wei's single most-quoted line and is routinely cited to 'Ask the Awakened: The Negative Way' (1963), where it appears in the opening/epigraph material. My recollection of that book association is firm but I cannot confirm the page, so a human should spot-check the citation before it is treated as primary-source verified. No competing attribution exists; the phrasing ('and there isn't one') is distinctively his.