still waters run deep

Quiet people have interesting, profound, or complex thoughts. No, Sarah is actually one of the smartest people in the company. She may not talk or socialize much, but still waters run deep.

Prov. Quiet people are often very thoughtful. Jill: I get the impression that Nathan is not very smart. He never says anything. Jane: Don't be so sure. still waters run deep, you know.

A quiet person may be very profound, as in Susie rarely says much, but still waters run deep. The physical observation in this term dates from ancient times, but it has been used figuratively since about 1400. Anthony Trollope amplified it in He Knew He Was Right (1869): "That's what I call still water. She runs deep enough. . . . So quiet, but so-clever."

People say still waters run deep when they are talking about someone who is quiet and speaks little, to suggest that they are in fact interesting and complex. He's extremely shy and withdrawn, though it may be that still waters run very deep.

A silent person may be a profound thinker; also, the quiet conspirator is the most dangerous. The expression has been a proverb in English since the fifteenth century and has counterparts in ancient Rome as well as in other countries. The analogy to the deep thinker is made plain in Anthony Trollope’s novel He Knew He Was Right (1869): “That’s what I call still water. She runs deep enough . . . So quiet, but so—clever.” The other meaning, with its implication of danger, is also put as “Beware of a silent dog and still water,” a translation of a Latin proverb that appeared in Thomas Fuller’s Gnomologia (1732) and later proverb collections.