Knowing where to Tap

Robert G Allen, in his book, relates a story about a factory owner who had an important piece of equipment break down that could shut down production and result in serious losses. He calls a technician to repair it. The technician arrives, examines the machine, takes out a hammer and delivers two taps and gets the machine working. He then presents his bill for $500. The factory owner is furious that he is being charged so much for two taps of a hammer and demands an itemized bill. The next day he received the bill that reads:

"Tapping with hammer $1. Knowing where to tap $ 499" Experience is valuable. Know where to tap!