Brain imaging techniques now let us observe mental fatigue in real-time, revealing that the brain, like muscles, grows tired from sustained effort. Mental fatigue arises when your brain senses it will run out of resources if it continues working at the same intensity. One way this might happen is when brain cells use up resources faster than they are being replenished. Your brain tries to remedy the situation by disengaging its attention, and you might experience this as your mind wandering away from what you are trying to focus on and being drawn towards lighter work and easier decisions. If you find yourself getting mentally fatigued often, try taking breaks often, limiting the amount of intense work you do in a day, and when all else fails, use motivation to push through.
