The classic chengyu
庸人自扰 ("a mediocre person creates trouble for themselves") comes from the Tang-dynasty 《
新唐书·
陆象先传》 — the Tang minister Lu Xiangxian's line that pointless worry is the hallmark of an ordinary mind.
庸 itself means "common, mediocre," hence
平庸 (mediocre),
庸俗 (vulgar).
