I totally agree with @silmathoron. Bill Gates might be a drop out, but this guy knows how to learn. After all, what is a PhD in an area? Monk-like focused mental effort to study an area deeply. You can achieve that either by yourself (Bill Gates does that), or by going to school (the path for the rest of us). Listening to this gentleman over the last years, I think his knowledge is deep and often not recognised. I have a great respect for him.