Carol Dweck, Daniel Coyle, and Noel Tichy all point out that you need to stretch to learn new things.
First, this passage from Carol Dweck …
My colleagues and I have conducted interventions with adolescents in which they learn that their brains and intellect are malleable. They discover that when they stretch themselves to learn new things, their neurons form new connections and they can, over time, enhance their intellectual skills. Compared to a control group that learned only study skills, these students showed marked improvements in motivation, and their declining grades were sharply reversed. Researchers Catherine Good and Joshua Aronson have found similar effects. In studies led by David Yeager, high school students who were taught a malleable view of their intellectual and social skills showed positive changes in their grades, stress level, conduct (including aggression), and health that lasted over the course of the school year.
Second, this passage from The Little Book of Talent: 52 Tips for Improving Your Skills:
There is a place, right on the edge of your ability, where you learn best and fastest. It’s called the sweet spot. … the underlying pattern is the same: Seek out ways to stretch yourself. Play on the edges of your competence. As Albert Einstein said, “One must develop an instinct for what one can just barely achieve through one’s greatest efforts.”
The key word is “barely.”
Finally, this passage from Deliberate Practice:
Noel Tichy, professor at the University of Michigan business school and the former chief of General Electric’s famous management development center at Crotonville, puts the concept of practice into three zones: the comfort zone, the learning zone, and the panic zone.
Most of the time we’re practicing we’re really doing activities in our comfort zone. This doesn’t help us improve because we can already do these activities easily. On the other hand, operating in the panic zone leaves us paralyzed as the activities are too difficult and we don’t know where to start. The only way to make progress is to operate in the learning zone, which are those activities that are just out of reach.
Update: This passage from The Art of Learning fits as well:
Usually, growth comes at the expense of previous comfort or safety. The hermit crab is a colorful example of a creature that lives by this aspect of the growth process (albeit without our psychological baggage). As the crab gets bigger, it needs to find a more spacious shell. So the slow, lumbering creature goes on a quest for a new home. If an appropriate new shell is not found quickly, a terribly delicate moment of truth arises. A soft creature that is used to the protection of built-in armor must now go out into the world, exposed to predators in all its mushy vulnerability. That learning phase in between shells is where our growth can come from.