One summer, Cao Cao was leading his troops in a punitive expedition against Zhang Xiu. It was extraordinarily hot. The burning sun was like a fire, and the sky was cloudless. The soldiers were walking on the winding mountain paths. The dense forest and the hot rocks exposed to the sun on both sides of the paths made the soldiers feel suffocated. By noontime the soldiers' clothes were wet through with sweat, and the marching speed slowed down. Some solders of weak physique even fainted on the roadside.
有一年夏天，曹操率领部队去讨伐张绣，天气热得出奇，骄阳似火，天上一丝云彩也没有，部队在弯弯曲曲的山道上行走，两边密密的树木和被阳光晒得滚烫的山石，让人透不过气来。到了中午时分，士兵的衣服都湿透了，行军的速度也慢下来，有几个体弱的士兵竟晕倒在路边。

Seeing that the marching speed was slower and slower, Cao Cao was very worried because he feared that he might bungle the chance of winning the battle. But how could they quicken their speed? Cao Cao at once callde the guide and asked him on the quiet whether there was a source of water nearby. The guide shook his head, saying that the spring water was on the other side of the mountain, which was very far to have to make a detour to reach. Cao Cao realized that time didn't permit them to make such a detour. After thinking for a moment, he said to the guide, "Keep quiet. I'll find a way out." He knew that it would be to no avail to order his troops to quicken the steps. He had a brain wave and found a good solution. He spurred his horse and came to the head of the column. Pointing his horsewhip to the front, Cao Cao said, "Soldiers, I know there is a big forest of plums ahead. The plums there are both big and delicious. let's hurry along, and we will reach the forest of plums after bypassing this hill." When the solders heard this, they immediately slobbered. Picturing in their minds the sweet and sour flavour of the plums, the soldiers felt as if they were actually eating the plums, the soldiers felt as if they were actually eating the plums themselves. The morale greatly boosted, the soldiers quickened their steps a great deal automatically.
曹操看行军的速度越来越慢，担心贻误战机，心里很是着急。可是，眼下几万人马连水都喝不上，又怎么能加快速度呢？他立刻叫来向导，悄悄问他：“这附近可有水源？”向导摇摇头说：“泉水在山谷的那一边，要绕道过去还有很远的路程。”曹操想了一下说，“不行，时间来不及。”他看了看前边的树林，沉思了一会儿，对向导说：“你什么也别说，我来想办法。”他知道此刻即使下命令要求部队加快速度也无济于事。脑筋一转，办法来了，他一夹马肚子，快速赶到队伍前面，用马鞭指着前方说：“士兵们，我知道前面有一大片梅林，那里的梅子又大又好吃，我们快点赶路，绕过这个山丘就到梅林了！”士兵们一听，仿佛已经吃到嘴里，精神大振，步伐不由得加快了许多。

This story comes from "The Fake Tangery" in Anecdotes of This World by Liu Yiqing of the Southern Dynasties period (420-589). From this story, people have derived the set phrase "quenching thirst by watching plums" to refer to trying to comfort oneself of others by idle dreams.
故事出自《世说新语·假谲》。成语“望梅止渴”，比喻用空想安慰自己或他人。