Another thing that I have seen and personally done that is a bit different...
"Comfortability in the process."
New people who are trained well often take extra care because they don't want to be the one who screwed up. "Old Heads" often know their job so well they do it out of sheer repetition. Its that middle ground, where you aren't new or old, but you still think you know the procedure. At this point you are just going through the motions, and you miss one step. Sometimes it is not putting on a turn signal, sometimes it is forgetting to completely secure your load (I'm a truck driver). Either way, as I called it, comfortability in the process. It can go completely unnoticed, or known to the perpetrator but not reported, or cause an incident whether minor or major. These can be very dangerous and if not kept in check as well, could lead to serious mishaps...
Casey