Lucy's Myth: But it's 92%, Not 10%

Sci-Fi myth: In the movie Lucy: Humans use only 10% of their brain capacity. Thus, a drug may give humans like Lucy superpowered brain function by allowing them to use more! It's amazing!

Reality: We use essentially all of our brain capacity. Some studies have shown that loss of 50 to 100 ml of brain out of about 1130 ml total brain volume is enough to cause cognitive impairment. So normal function would require that we use at minimum 92% of our brain capacity. Furthermore, it's likely that impairment sometimes happens even with less than an 8% volume loss. At least, the patients notice it.

Of course, a drug that made Lucy a mere 8% smarter, enough to perhaps, with the right help, defeat her opponents using ordinary means, would not make much of a movie.

Gotta love those scfi-fi movies though. Great entertainment, just misleading pseudoscience in their premisses (and on their premises).