It's all in the head 

There is an anecdote told of a prisoner in a Russian labor camp. His task, for twenty-five grueling years, involved turning a heavy wheel fixed to a wall. He assumed perhaps he was milling grain, or pumping water that irrigated many fields. In his mind's eye he saw the plentiful crops and the sacks of milled grain feeding thousands of people. However, upon his impending release, he requested to see the apparatus behind the prison wall. To his dismay, the wheel served no purpose. The man collapsed in a faint, absolutely devastated. His years of toil felt utterly futile.