A man from the state of Chu was crossing a river. In the boat, his sword fell into the water. Immediately he made a mark on the boat.
"This is where my sword fell off," he said.
When the boat stopped moving, he went into the water to look for his sword at the place where he had marked the boat.
The boat had moved but the sword had not. Is this not a very foolish way to look for a sword?

战国时，楚国有个人坐船渡江。船到江心，他一不小心。把随身携带的一把宝剑掉落江中。他马上掏出一把小刀，在船舷上刻上一个记号，说：“这是我宝剑落水的地方，所以我要刻上一个记号。”

船靠岸后，那楚人立即从船上刻记号的地方跳下水去捞取掉落的宝剑。捞了半天，仍不见宝剑的影子。其实他又怎么找得到宝剑呢？船继续行驶，而宝剑却不会再移动。像他这样去找剑，真是太愚蠢可笑了。