- Frustration is not a sign that you're not learning; ease is. For learning to happen material needs to have some level of difficulty. - We can include this difficulty by increasing complexity or by interleaving material or any other strategy. --- What you want is to make it easy to make it hard.” Kornell was explaining the concept of “desirable difficulties,” obstacles that make learning more challenging, slower, and more frustrating in the short term, but better in the long term. - David Epstein in [[Range]]