People only use 10% of their brains.

Yeah. I want to punch every single person that says that. Because it is not a complete fallacy, but the way it is used and what it implies annoys me.

So first lets us consider the brain.

What does your brain contain? Hundreds of specialized areas, each containing neurons specialized in specific tasks. Different areas of the brain are used for different reasons. So unless you need to make love to a person you hate while looking at a person you love, listen to music, smell the flowers, skip around, calculate the 3-step moving average of a time series, recite a poem, chew an apple, sense every muscle of your body, and keep track of your orientation since you are doing these things inside a moving van; unless you are doing all of that, at the same time, you will rarely have more than 10% of your brain-mass showing signs of activity at the same time.

But: your brain does tend to overload during R.E.M. and the activity gets to percentages over 10%. So the statement has a problem. Is this 10% an average percentile we are interested in?

Let us assume it is an average percentile. Why on earth would we want to, on average, use more of our brain? The aditional active areas will not change their specialization! What good is it to me to use the part of my brain that flaps my arms when I am trying to read a book? Not good at all, that is the kind of good it is.

However I am not against having the people who are using this argument actually get a 20% increase of brain-mass activity! Because if they do, this is what is going to happen: More areas in the brain will be working, consuming huge amounts of energy, and transforming a great deal of it into heat. This heat will then melt their brains, and we will be left with fewer people who repeat this stupid phrase.

Cogito cum XXX% caput meum, ergo liquefactus sum.