It's a notion that's been propagated by movies, magazines, and motivational speakers and repeated by well-meaning folks and shysters alike. They tell you that you are only using 10% of your brain. If you are only able to access a fraction of your brain power, just imagine what you could do if you tapped into all that unused potential. Read other people's thoughts, play the stock market, crush cans with your mind and levitate. Not to rain on your brain parade, but that 10% stuff is so far off that it would be laughable if it were not so widespread, and I kind a can't believe I'm still talking about it.
So like many myths, it's hard to pinpoint exactly where it began. There is no definitive source, though some have linked it back to the American Psychologist William James and even Albert Einstein, who both suggested, in so many words, that we were only using part of our mental potential.
But the fact is, we is pretty much every part of our brains. A lot of it is active most of the time, whether you are reading a book, or listening to music, or walking around town or even sleeping. How can we be so sure? For one thing neuro-imaging techniques like PET scans and MRIs actually let us see the brain in action. This images show as that nearly every region of the brain lights up during even simple tasks, like walking and talking. While, we don't use all of brain at once, just like we don't engage every single muscle at the same time, those scans prove that over the course of any given day you use just about all of your brain. It also stands to reason that if 90% of your brain was useless, you could remove large portions of it, as you might an appendix or tonsil, and carry on as usual. Brain damage and disease wouldn't be as much of a concern if only 10% of the organ was actually functional. But, in reality, there isn't a single area of the brain that can be damaged or diseased without resulting in some kind of physical or mental consequence, small or big.
You may have heard of the case of Phineas Gage. the 19th-century railroad worker, who wound up with a spike through his head because of an accident. It actually didn't stay in his head, it went all the way through and then kept going for a quite while. It didn't kill him, somewhat surprisingly, and he still had his memories and his skills. But many of his friends reported that he had changed personalities. Now we don't actually know a ton of Gage, because a lot of people used him to try and prove a lot of different of points over the years, but there is little doubt that you can have a rod go through your brain and not have somethings messed with.
Then, there is Clive Wearing, the British Pianist, who had a viral infection that destroyed his hippocampus, the part of the brain that controls the storage of memories. As a result, he is no longer able to recognize anyone but his wife, and he can't retain a memory for more than 30 seconds at a time.
Every part of your brain has a function, and you need it in order to keep being you. Finally, we know that our brains are working all the time because we have to constantly feed them, literally. The average human brain accounts for about 3% of a person's body-weight, but it demands at least 20% of the body's energy to keep all those neurons firing. We are talking hundreds of food calories every day just so your brain can remind your heart to beat, or help you solve for X, or remember where you left your phone. Our constant need for food, especially foods rich in fats and sugars, has a lot to do with our brains. It wouldn't make much evolutionary sense for us to expend so much energy feeding a useless, wet lump. So, in the end, while telekinesis would be pretty awesome, our brains are already capable of truly incredible things. In fact, if anything, we only understand a fraction of what's going on up there, so instead of insulting its function, be thankful for all that your brain does, which is more than you know.
source ; scishow