Do you find you more often leave things behind when customers help you to take things back outside to your van? I do.!
It's like you lose track of where you are up to.
Either that or it's pouring with rain when you arrive but sunny by the time you leave and aren't expecting to put a coat on.
Oh, and finally, I've had clients tidy up my coat and put it on the coat stand. If they had left it where I had left it I wouldn't have forgotten it.