After laying down a nice white base coat, I looked around for a mixing cup for the clear and settled on a new, clean coffee can. Clear, reducer and hardener were all strained going into the can, but the mix went straight into the gun.
Spraying out onto the fender it seemed like I was getting specks in the paint and couldn't figure out what was up...then blammo it was like instant metallic spreading out over my white. Turns out the plating inside the coffee can came loose into the clear. A nice mess to stop and clean up, instead of continuing on with my painting.
Another mixing cup story was, pouring paint into some regular plastic cup that was laying around. It sat for maybe 20 minutes on the bench then when I went to pick it up it collapsed in my hand, melted. Paint went everywhere while I stood there with that goo in my fingers.
Just an amateur here, my paint jobs (when I do one) come out good but it's from persistence more than skill. I've certainly made most of the mistakes.