This idiom comes from a story in ancient China:
A man was crossing a river by boat when his sword suddenly fell into the water.
He didn’t panic — instead, he took out a knife and carved a mark on the boat where the sword had dropped.
Later, when the boat stopped, he jumped into the water —
right where he had made the mark.
But of course… the boat had moved.
The sword was long gone.
The lesson?
You can’t solve a problem by holding on to a solution that no longer fits.