Rejection therapy is deliberately seeking small rejections until they stop hurting. By gamifying the 'no,' you desensitize the fear of negative evaluation that drives most social avoidance, so rejection stops quietly running your decisions.
Underneath most social fear is one engine: the dread of being judged. Rejection therapy attacks it head-on. You go ask for the unreasonable discount, the extra favor, the number, expecting a no, and you discover the no barely lands.
The reps recalibrate your threat meter. After enough small, survived rejections, the catastrophic weight you assigned to 'no' deflates. Practicing the ask first, out loud and safely, makes that ladder a lot easier to start climbing.