there is an old story that exists in numerous variants and goes roughly like this:
A town’s electricity generator failed and various engineers were unable to fix it, so an elderly electrician was summoned. He examined the generator carefully, then tapped it lightly once with a hammer, and power was instantly restored. He submitted his bill for $1,000 and as he was asked for the explanation, answered: “Tapping — $1. Knowing where to tap — $999.”
A town’s electricity generator failed and various engineers were unable to fix it, so an elderly electrician was summoned. He examined the generator carefully, then tapped it lightly once with a hammer, and power was instantly restored. He submitted his bill for $1,000 and as he was asked for the explanation, answered: “Tapping — $1. Knowing where to tap — $999.”