Why do we do things? What persuades us to put an effort to achieve goals, however mundane? What, for instance, drives us to search for food? Neurologically, the answer is hidden in the reward system of the brain—an evolutionary mechanism that controls our willingness to work or to take a risk as the cost of achieving our goals and enjoying the perceived rewards. In people suffering from depression, schizophrenia, or Parkinson’s disease, often the reward system of the brain is impaired, leading them to a state of diminished motivation for work or chronic fatigue.