I never believed in that whole (read in a whiny voice) "Humans only use 10% of our brains" thing. 

It's is pure silliness. The following vid (below) from discovery does a pretty good job of explaining why. 

More reasons I don't believe this:

  1. The alleged originators of this theory put it forward in the 1890s. Are we really giving credence to a theory "discovered" during a time when bloodletting was still a thing? Before antibiotics? Before vaccinations?
  2. Dale Carnegie (the guy who made this theory famous) was a self-help salesman. Seems to me like he had a dog in this hunt.
  3. If I'm only using 10% of my brain why did it get so tired after chemistry tests? My muscles don't get that tired after using 10% of them. My skin doesn't burn after being exposed to only 10% sunshine. 
  4. If I know anything about the human body it's this: if you don't use it, you LOSE it. 
  5. How is it that no other part of my body only uses 10% of it's capacity? I don't use only 10% of my eyeballs. I don't use only 10% of my bones. If I do only use 10% then I generally become very ill (see reason #4).
  6. It's insulting to me to imagine that the entire population of earth, every human that has ever lived, has only ever used 10% of his/her brain function (Jesus? Mohammed? Tesla? Hawking?)
  7. If someone ever did figure out how to use their entire brain, how is it that they still never became intelligent enough to teach the rest of us to tap into the other 90% of our own?