There is always some progress, even when things are at their worst, because then you don't have to do over again all the negative things you've already done. -- Alberto Giacometti
Through an unlikely and unintended set of circumstances I met a fit and weathered man a few years my senior. While showing me around his goat farm, he referred in passing to his boat, and, intrigued, I asked him about it. He said he'd been building a 105' sloop for the past twenty years, and was still working at it. I said I wanted to have a look. Within an hour my son and I were trying to be of some use and trying not to get caught up in the lines. I expressed my admiration for what he had accomplished, and he suggested what he had learned in the process of building a boat for past twenty years -- "I know how not to build a boat."
I learned to make etchings pretty much on my own. I even tried things out on students in my classes and learned from their mistakes, which were of course my own mistakes. I learned lots of ways to do things wrong.
I wonder about the value of telling students they're making a mistake, even while they're making one. I used to tell students exactly how not to do something, and then they would decide to listen and do just what I told them not to do. So I stopped telling them and let them make their own mistakes. Mistakes are things you learn not to do again; you have no reason to even to think about them again. Mistakes in art generally have little consequence; no one gets harmed, except maybe some art supplies.
But avoiding mistakes doesn't create something beautiful or useful, let alone a 105' sloop.