Michael Mosley puts his own body through a series of experiments to find out how pleasure and pain actually work in the brain. He eats the hottest chilli pepper in the world on camera, tracking how the burn triggers a rush of endorphins and why some people come back for more. He talks with researchers about the flood of feeling new parents get when they hold a newborn, and what that surge is doing evolutionarily. On the pain side, Mosley submits to controlled experiments designed to measure how much discomfort he will tolerate for a reward, and what that threshold reveals about willpower and motivation. Experts weigh in on rare cases of people who cannot feel pain at all, and what their lives show about pain's actual function as a warning system rather than just an unpleasant sensation. The film keeps returning to one practical question: how much pain is worth enduring for a given pleasure, and does that calculation change person to person.