Making his mark -- Acting foolishly（刻舟求剑）
Once, a Chu person (Chu is one of the seven hegemonic states of the period of the Warring States in 11th century BC-223 BC) was crossing the river by boat. Carelessly, he dropped his sword into the water and he immediately made a mark on the boat.
"This is where my sword fell" he said. After the boat stopped, he jumped into the river to look for his sword.
The boat had moved, but the man's sword had not. Isn't this a foolish way to look for a sword? Future generations use this analogy to illustrate people who are inflexible and stubborn.
kè zhōu qiú jiàn