On June 26, 1940, as Britain was girding for the onslaught of the Luftwaffe after the fall of France, Clementine Churchill wrote her husband, Winston, an admonishing note.

“There is a danger of your being generally disliked by your colleagues and subordinates because of your rough, sarcastic and overbearing manner,” she warned the prime minister, who was otherwise preoccupied by the prospect of imminent Nazi invasion, a scheming foreign secretary, a restive backbench, and the absence of material support from the United States.

“I have noticed a deterioration in your manner, and you are not so kind as you used to be,” she continued. “It is for you to give the orders and if they are bungled — except for the King, the Archbishop of Canterbury and the Speaker — you can sack anyone and everyone. Therefore with this terrific power you must combine urbanity, kindness and if possible Olympic calm.”

Clementine concluded by citing a French proverb, “One can reign over hearts only by keeping one’s composure.” Winston got the message and found ways to make amends. As his private secretary, Jock Colville, later recalled, “When he was at No. 10 there was always laughter in the corridors, even in the darkest and most difficult times.”