mastery is knowing where to tap
There was once a company which had a boiler system that wasn’t working properly. After days of sputtering and hissing, a boilermaker was called in to fix the problem. He listened carefully to the engineer’s description of the issues at hand and after asking a few questions, he went straight to the boiler room. He looked at the maze of twisting pipes, listened to the thump of the boiler and the low hiss of escaping steam for a few minutes, occasionally touching some of the structure thoughtfully. Then while humming softly to himself he reached into his small black bag and pulled out a tiny hammer. He tapped a bright red valve, just one time and instantly, the entire system began working perfectly. Then the boilermaker went home.
When the owner of the company received a bill for $10,000 he was confused as the boilermaker had only been in the engine room for less than ten minutes. So he requested an itemized bill and this is what the boilermaker sent him:

Tap with hammer: $ .50
For knowing where to tap: $9999.50
Total: $10,000.00

Change happens in an instant. Mastery is knowing where to tap.