Marking the Boat to Locate the Sword
A man of the state of Chu was ferrying across a river when his sword fell into the water. He lost no time in marking the side of the boat.
"This is where my sword dropped," he said.
When the boat morred, he got into the water to look for his sword by the place which he had marked. But since the boat had moved while the sword had not, this method of locating his sword proved unsuccessful.
The Discourses of Lü Buwei
(Lv Shi Chun Qiu)