This idiom comes from the philosopher Mencius (
孟子), who criticized the thinker Yang Zhu (
杨朱) for extreme individualism. Mencius said:
杨子取为我,
拔一毛而利天下,
不为也 — 'Yang Zhu wouldn't pull out a single hair even if it would benefit the whole world.' Over 2,000 years later, it's still the go-to insult for cheap people.