Literally 'carve the boat to find the sword' — from a fable where a man drops his sword in a river and marks the boat's side, then dives in when the boat reaches shore, expecting to find the sword at the mark.
Using old methods to solve new problems is like marking the boat to find the sword.
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This idiom comes from Lü Buwei's《吕氏春秋》(3rd century BC). A man from Chu dropped his sword overboard, marked the spot on the boat, then tried to retrieve it from the mark after the boat had moved on. It's taught to every Chinese schoolchild.