Overall, I think Ericsson has done an ok job of introducing the layman to the field of deliberate practice. To recap: practice works because the human brain is adaptable, and because performance is determined by the quality of our mental representations. Naive practice is bad; don’t do it. Purposeful practice is all we have if we are to work in a field with no developed training methods. Deliberate practice exists where fields are well developed, and require a teacher to execute well. Creating deliberate-practice-inspired training programs are extraordinarily difficult, and you should expect such efforts to be doable only with extended trial and error.
But what Peak fails to do is to provide a complete guide on how to put deliberate practice into … well, practice.