I hand filed for 12 years before I learned what it takes to do it right. And in that 12 years I was just going through the moves and not paying attention to the details. That's when I was doing line clearance work 30 years ago.
Today I can touch up a chain and get it cutting satisfactory, and I can sharpen a chain and get it cutting like a raped ape. Big dif between the two.
First thing, and most important is, you need a good chain to begin with. All a person can do with a wore out chain is touch it up, and make it cut satisfactory.
Falling and bucking trees by the bushel taught me that. What you can get by with doing private tree work will break you working by the bushel in the woods. The only way you're going to make money cutting by the bushel is to have a chainsaw that cuts like a raped ape. And I said chainsaw. The chain is but one part. The saw must run dependably and efficiently, and the bar must be true. Without either the chain will not make up for it.
In the woods it was, "learn how to sharpen and cut, or die of starvation trying."
Unfortunately a person of experience can speak volumes about the details of chain sharpening and the beginner isn't going to pick it up until that certain something clicks in their brain, or in their stomach.