“It is estimated that most human beings only use 10% of their brain’s capacity,” says Morgan Freeman’s character from a lectern in Lucy. It is a widely-believed myth, oft repeated, both in science fiction and in self-help literature.
So do human beings only use 10% of their brain capacity? I’m afraid not. This is one that falls squarely in the fiction category. The myth even has its own wikipedia page. Considering how many times it has been debunked, it’s surprising how persistent it is. And if it is not 10%, then it is 35% (or some other random number below 100%). The truth is, however, that most of the brain is in use most of the time.
Here’s a summary in 3.06 minutes, which also covers some of the superpowers in Lucy:
Now, is the reverse true? Could you get by using less of your brain? Yes, sort of, in some cases. Plenty of people live with reduced brain matter (it is a common consequence of aging, after all), without any apparent problems. If the reduction happens over time, the tissue that remain can often compensate nicely. But you’ll still use most of your remaining brain most of the time.