army officer and author 1752-1825
Philip Stanhope, 4th Earl of Chesterfield (22 September 1694 – 24 March 1773) was a British statesman and man of letters.
From: Wikiquote (CC BY-SA 4.0)
Listen to everything that is said, and see everything that is done. Observe the looks and countenances of those who speak, which is often a surer way of discovering the truth than from what they say. But then keep all those observations to yourself, for your own private use, and rarely communicate them to others. Observe, without being thought an observer, for otherwise people will be upon their guard before you.