Back in the day before trade colleges came along you needed to have a mentor to learn a trade.
At that time, everything came through experience and first hand know-how.
There weren’t Youtube videos, or even truly many books, on how to learn trades like smithing or carpentry. Since the start of trade colleges, the mentor system of studying a trade has gone by the wayside, regulated out of existence or damn close to it. The government says people need standardized tests to prove someone’s level of skill, which is patently ridiculous. Job was fortunate enough to have a mentor who taught him the basics of HVAC work when he was still a teen. His next door neighbor was a lady named Big Sal, and she did mobile heating repairs out of her van. Big Sal was self taught, and knew everything there was about air duct and gas furnaces. She even made her own sheet metal in her workshed, so that she’d craft her own custom air ducts. Big Sal did not know anything about the air conditioner. That was “after her time” she consistently said, although she taught him the basics of heating repair, and the skills Job needed to make his own air duct. Later he’d go to college to become certified officially, and that is where he started studying about air conditioners. Jake was already an expert in gas furnaces and ventilation systems, although he had a lot to learn about AC. His mentor taught him a lot, but Job got the rest of the way through taxing work.