Good question. Retention was always a problem for me as well. I have to read the important concepts a couple of times and them try to implement them right away so they stick.
Its like when I am learning a new program or piece of equipment. I can read the instructions but I have to do it a couple of times to retain it. Here is a shot of me and a typical piece of equipment I operate...
When I am not selling books
Actually this is the older model. Have to learn a new ones all the time.