Once you find a solution, you stop looking for a better one
Luchins had people solve a string of water-jug puzzles that only worked with one specific three-step formula, then quietly slipped in puzzles solvable in a single obvious step. Most people kept grinding through the long formula anyway, blind to the shortcut sitting right in front of them. He called it the Einstellung effect: a mental rut built by your own past success.