Motivation is an internal state that propels individuals to engage in goal-directed behavior. It is often understood as a force that explains why people or other animals initiate, continue, or terminate a certain behavior at a particular time. It is a complex phenomenon and its precise definition is disputed. It contrasts with amotivation, which is a state of apathy or listlessness. Motivation is studied in fields such as psychology, motivation science, neuroscience, and philosophy.