望梅止渴 (wàng méi zhǐ kě): lit. to quench one's thirst by thinking of plums; fig. to console oneself with illusions

wàngméizhǐ

lit. to quench one's thirst by thinking of plums; fig. to console oneself with illusions

Cao Cao told thirsty troops of plums ahead, and their mouths watered enough to march on. For comfort that is imaginary but works.