Acharya Prashant explains that the brain, like any other part of the body, consumes significant energy and experiences fatigue when used for intense intellectual work. He clarifies that entertainment is not the same as rest; while entertainment merely suppresses or postpones stress like a painkiller, true rest or 'Vishranti' eliminates it. Spirituality is described as the art of attaining this true rest. He emphasizes that while the body and mind will inevitably tire due to their mechanical and biological nature, the inner self of a person devoted to the right cause does not experience exhaustion in the same way.