He was still wearing his nametag from a nearby trendy science & technology conference. john Trouble. With a capital T, but (pretentiously enough) a lowercase j.
He sat down uninvited.
"I need your help," he said, "I just heard that people only use 10% of their brain. I want to be smarter than that. I want to use 100% of my brain. Can you help me, gumshoe?"
Okay, I admit it, I was wearing a nametag from the same conference, and "gumshoe" was written with a pretentious lowercase g. But anyway this really got my goat.
"That statistic is kind of sorta accurate, but deceptive," I said, "You do indeed only use 10% of your brain at a time, but not the same 10%. Like, uh, there's a part of your brain that connects smells to memories -- if you're not smelling anything nostalgic, that part is dormant, and why wouldn't it be? There's a part that recognizes faces, and another part that puts inflection and emotion into your voice, and another part that takes red and green visual receptors and combines them into yellow. Those parts aren't supposed to operate all the time. You use the parts of your brain that you need. If you were really using 100% of your brain, I'm pretty sure that all you'd get would be a really painful grand mal seizure."
He looked crestfallen.
"Don't look so crestfallen," I said, "There are still things you can do to enhance mental performance. You can eat more vegetables, for instance, and find out if you have any mild food allergies and avoid those. You can make regular use of Dual N-Back exercises. You can put more plants and brain toys into your environment to encourage neurogenesis. You can go back to school and study logic and epistemology and literary analysis and business and computer science and definitely not evolutionary psychology and calculus and cultural anthropology, to get more perspectives on things."
"Those sound hard," he retorted, as if he'd just proven me wrong.
"Most of all," I said, "You can cultivate a sense of humility about the world, and learn to admit that you don't already know the answers, so that you can seek them out."
"But... but... my name is Trouble!" he said, "With a Capital T!"
"And that rhymes with N! And that stands for neurogenesis!" I replied eagerly.
I think that convinced him.