During the Three Kingdoms Period (220--265), Liu Pei, heir to the house of Han, was once forced to seek refuge with Ts'ao Ts'ao, the wily general and prime minister of the North.
One day Ts'ao Ts'ao ordered a subordinate of his to ask Liu Pei to come to his residence.
"I saw that the plums in the back garden have ripened," Ts'ao Ts'ao told Liu Pei, "and it made me think of the time my troops and I were marching in a waterless region."
"All the soldiers were thirsty, but I thought of a trick. I pointed ahead with my whip and said, 'Up ahead is a grove of plums, sour and sweet, which will quench your thirst.' When the soldiers heard this, the thought of the plums made their mouths water, and they stopped feeling thirsty. Soon after, we came to a place with water.
"Because the plums in the garden are ripe, I've invited you here to enjoy some with me and drink some wine."
The expression "quenching one's thirst by thinking of plums" has since been used to describe consoling oneself with false illusions or feeding one's hopes on a fancy.