Look what Aleksandr Solzhenitsyn wrote in The Gulag Archipelago about how the Soviets extracted much extra labor from prisoners for little extra reward:
Percentages above 100 conferred the right to supplementary spoonfuls of kasha (those previously taken away). What a merciless knowledge of human nature! Neither those pieces of bread nor those cereal patties were comparable with the expenditure of strength that went into earning them. But as one of his eternal, disastrous traits the human being is incapable of grasping the ratio of an object to its price. For a cheap glass of vodka a soldier is roused to attack in a war not his own and laws down his life; in the same way the zek, for those pauper’s handouts, slips off a log, gets dunked in the icy freshet of a northern river, or kneads clay for mud huts barefoot in icy water, and because of this those feet are never going to reach the land of freedom.
The Gulag Archipelago, Volume 2, p 156