Brain retraining is not about tolerating milder intrusive symptoms.
It's about learning that symptoms can be generated by the brain as a warning signal that it doesn't need to send (the idea is it can become over sensitised in certain conditions, such as when someone has experienced trauma or has a particularly sensitive temperament). The techniques acknowledge your symptoms are real but teaches you how to dampen down the brain's sense of being under threat so they stop. The symptoms go, you aren't ignoring anything or tolerating anything.