No one ever said that. It's either misquoted or mistranslated. Albert Einstein once said, in German: "Wir nutzen nur zehn Prozent unseres geistigen Potentials." Translation: "We only use ten percent of our mental (meaning: intellectual) potential." Turning on the TV and watching for 5 minutes will tell you this is very optimistic. At least you will agree he has a point. I don't know when this became misunderstood as some bogus neurobiological statement.