10% of brain control is a lie.
Our brain consumes %20 percent of our bodys energy so if we could control our brain at %100 we would need %200 of our bodys energy we dont have that much energy and we cant carry that.Lets say we somehow got that much energy , it will cause our brains grow more and cause that our skulls crush.
I accept as true with you a person can never completely control his brain during this case his death is inevitable. Bren never wanted to require the pressure off of himself. She always wants to hold less pressure therein case if people have 100% control then the brain will worsen and go crazy.