" Many teachers believe that if they can make learning easier and faster, the learning will be better. Much research turns this belief on its head: when learning is harder, it’s stronger and lasts longer. It’s widely believed by teachers, trainers, and coaches that the most effective way to master a new skill is to give it dogged, single-minded focus, practicing over and over until you’ve got it down. Our faith in this runs deep, because most of us see fast gains during the learning phase of massed practice. What’s apparent from the research is that gains achieved during massed practice are transitory and melt away quickly. "

― , Make It Stick: The Science of Successful Learning