discretion

be the soul of discretion

to be good at not talking about things that other people want to keep secret. As regards Nigel, he's the soul of discretion. I'm quite sure he won't mention this to anyone.

See also: soul

Discretion is the better part of valour. (British & Australian, literary, American & Australian, literary)

something that you say which means that it is better to be careful and think before you act than it is to be brave and take risks. She decided not to voice her opposition to the Chairman's remarks. Perhaps discretion was the better part of valour.

See also: better, part