Growing up around the work.
I grew up in southwest Georgia in a family that did outdoor service for a living. My grandfather did it. My father did it. I was the kid who got handed a shovel at twelve and told to go dig where the line was. That's how you learned — by watching, by doing it wrong, and by having someone older than you explain why the way you just did it was going to leak in six months.
It was a slow, serious apprenticeship. Nobody handed me a certification and called me a professional. I had to earn trust one job at a time, starting with the easy stuff and working my way up to the jobs where getting it wrong meant tearing up a lawn twice.