Perhaps the best explanation is this short story.
A ship engine failed. No one could fix it. Then they brought in a man with 40 years on the job.
He inspected the engine carefully, top to bottom. After looking things over, the guy reached into his bag and pulled out a small hammer. He gently tapped something.
Instantly, the engine lurched into life. The engine was fixed!
Seven days later, the owners got his bill for $10k
“What?!” the owners said. “You hardly did anything. Send us an itemized bill.”
The reply simply said: “Tapping with a hammer. $2. Knowing where to tap? $9,998.