What quote or saying do people spout but is complete BS?

Humans only use 10% of their brain.

This is an absolute scientifically proven myth. Doctors over a century ago noted that head damage and trauma patients could still function relatively normally so they assumed that humans could live with 10 percent of the brain. Modern science now knows that the brain does a great job of rewiring neurons to compensate for damage. We can map brain activity and it's been proven that over time nearly 100 percent of the brain is used, with different parts going through cycles of activity. Despite this popular media still keeps repeating the same 10% myth like it is a fact.

Just hearing that myth being repeated makes me want to telekinetically hurl the person saying it across the room. It's that annoying.