Making His Mark 刻舟求剑

A man from the state of Chu was taking a boat across a river when he dropped his sword into the water carelessly. Immediately he made a mark on the side of the boat where the sword dropped, hoping to find it later. When the boat stopped moving, he went into the water to search for his sword at the place where he had marked the boat. As we know, the boat had moved but the sword had not. Isn't this a very foolish way to look for a sword?

楚国有个人坐船渡江时，他不小心把自己的一把宝剑掉落江中。他马上掏出一把小刀，在宝剑落水的船舷上刻上一个记号。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。他怎么找得到宝剑呢？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。