I knew someone with a Fedex run and it was so impossibly demanding and there were so many deliveries that he was always 2 hrs late getting home in the evening and he was always a nervous wreck. Those packages MUST be delivered. To Fedex that kid was wasting precious seconds....
I've heard from multiple sources, including employees of UPS, that UPS workers aren't given enough time to deliver their packages. Drivers are forced to "ease nature" in a container in their vehicle, to deal with the time crunch.
I wouldn't be surprised if FedEx was similar.