 The key to improving thinking, to thinking better, is to know more. So if you want to be a better singer, you have to spend time singing. Well the notion of desirable difficulties is that it refers to a set of manipulations that all have the property that they create challenges, a sense of difficulty during the acquisition process. We like to think we know how to learn, how we learn best, in what situations we learn best, and that we know when we've learnt something. We have no real insight into the basis of our behaviour. It's really difficult to predict what we'll learn and whether we'll be able to retrieve this stuff in the future. What we think works for learning. It's not even that there's no relationship between what we think and reality, but in fact it's a negative relationship. What we think works is the exact opposite of what actually works.