So what is really inaccurate is the inaccurate assumption that the 10% brainpower is a myth. Which it is not. At least not in the way I think the movie is trying to use it. It seems to be that what they are trying to state is that we only use 10% of our potential. And that make sense if you look at potential as related to IQ. The average IQ is 120 +/- so a person with an IQ of 200, 250, or 300 would obviously be using more potential than the person with an IQ of 120. Savants are a perfect example. They normally are suffering from damage in a particular part of the brain but because of this they end up having exceptional abilities that show what potential our minds have but are unable to use.