This is why you can't trust anyone to work on your car.

well, as a mechanic, I actually see People that should not have wrenched on they own cars as well! Im not defending shortcuts here..
Its not just the mechanics that destroy Things... :-) another thing is that at home you may have time to wait for that spare to show up, at work, everything takes time, and Labour is something the customer doesnt want to pay...

that said, we had a Young gun at Our shop that used the impact wrenc on a aluminum oil sump bold....I must say he was shocked when the Complete sump cracked in several pieces..LOL not so happy customer
True, it takes practice- which typically means screw-ups for most people to realize what they need to do.

Few years ago I got new tires on my truck at Goodyear. Being raised by a mechanic I just knew they overtightened the lug nuts with the impact gun, so I figured I'd break them loose with a breaker bar before going anywhere else after I got it home. I was 1/2 right - the rears were way tight, but all the fronts were finger loose and 1 was a different size. Tightened them up, removed the odd nut out and took it back to them for the correct one and told them about the loose ones. Service manager asked the gopher next to him what *** hole goes home and checks his lugs. I responded with a smarter one than the one who runs the shop. His face turned red and he was about to say something - I cut him off and asked if I'd been better to drive it until the wheels fell off and then I would own the shop. He walked away.

We all forget something sometimes. We are human. But at least own up to it.....lol
That's amazing. I had a similar one recently that reminded me that I need to do what I can and not let anybody sorry-assed charge money for anything that I'll end up needing to fix.