I worked as a medical claims examiner for almost 20 years. It almost killed me, because the job consisted of getting screamed at every single day by angry insureds, meeting production and quality standards that were just ridiculously hard, and putting up with psycho, back-stabbing co-workers...not to mention the guilt I felt from having to cut off people's medical benefits. I'm horrible at "multi-tasking" (whatever that means), and my temper is pretty explosive. So it was a hard road. The last ten years I was there, they moved me to working on attorney complaints, because my temper came in handy dealing with those bastards.
I haven't worked in 4 years. I want to go back to work, but I have no idea what I'd do. I was accepted into a masters in applied linguistics program, but I don't really want to go back to school. I have little confidence in my cognitive and "people" skills at this point in my life.
As for as why people don't do their best...in my corporate environment, it didn't pay to do your best. The harder you worked, the more they loaded on you, until you couldn't keep up and you'd find yourself demoted. It finally caught up with my company - it always catches up with them. But by that time, you're so burned out that the damage has been done.