I like the explanation, but I don't like the idea of telling everybody that things where different in the past. When most people were farmers they also worked more than 12 hours a day, since you need to take care of such a big place. When most people were factory workers people also worked more than 12 hours because the boss thought it would make him more money if you worked more (and with simple, mechanical work that's actually true). The kind of work changed, as well as the reason. But we always worked too much.

And there is one reason he didn't mention: When you don't work so much, you need to figure out what to do with your time. You can't watch movies all day. Nobody can do that for a long time. So you need to think hard about other reasonable things to do. And thinking is painful and scary.