"full employment" is a false goal - not so much that it's unachievable, but that it is unnecessary - at least unnecessary in economic terms, although the ruling class uses it for social control. They are afraid that if too many hands are idle, eventually those hands would end up around their necks.
(1) Primitive people spent their time just trying to get enough food to eat.
(2) Technology advances such that only a tiny part of the population is needed to gather enough food.
(3) People basically just sit around bored, looking for something to occupy their time.
(4) The troll is born. They instigate conflict just for laughs, while their victims fight wars.
(5) Some people get good at shutting down trolls, but then it's back to boredom again.
(7) The modern economy.