I tend to remember my successes and forget my failures, so I make a point of keeping visual reminders of some of my "goofs" to keep me humble. Such as:
- the two halves of a major wiring harness connector. They sit on a ledge above my toolbox at the dealership, each half sprouting a spaghetti-cluster of colored wires hacked off an inch from the back of the plugs. They remind me of a job I did where I told the customer it would cost X-dollars to diagnose the electrical problem in his machine, and an unknown amount to repair it, depending on what proved to be the cause of the problem. As predicted, it cost X dollars to diagnose the problem, but 4 times that amount to actually put things back together after tearing it into a million pieces to diagnose it. In the end, the customer refused to pay any more than the original amount I quoted him. He said he would have hauled the machine home in buckets and boxes rather than pay what it eventually cost to repair and reassemble it. So those two mangled plugs remind me to always make sure a customer actually wants his machine fixed before I fix it.
-On my desk here at home I have a bent, twisted, mangled metal dowel that's supposed to fit into a hole in an engine's flywheel to maintain timing while you're working on that engine. It's bent, twisted and mangled because I got in a hurry and forgot to remove it after I finished the repairs. The engine had enough torque to start and run, but only after mangling that pin. I was lucky to pry it out without major engine disassembly, but it's a reminder for me to always slow down after finishing repairs and take inventory of tools and accessories.
-I carry with me always a 2-inch scar on the outside of my right thumb, where a surgeon did micro-surgery to reassemble that thumb after it got caught/crushed in a home-made hydraulic press. Working in a farmer's shop, I was using his press to disassemble parts. He offered to help, somehow somebody lost their grip on a large piece of steel as I was re-positioning things on the press, and my thumb suffered the consequences. I'm not sure what that scar is supposed to remind me of--maybe that human body parts, for the most part, aren't replaceable. Which is probably a good thing to remember as I make a living around large machinery with lots of moving parts.