The way the author explains it above (mechanical) is the way I was initially taught over 20 years ago. However, it wasn't effective for my learning style because it felt random and incoherent. So _why_ does 'h' key move left? And _why_ do I have to press 'i' for "insert" mode when I didn't have to do that in Notepad/MSWord? My UNIX instructor couldn't answer those questions. He just said, "I dunno, it's just the way it is." As a sysadmin, I memorized it but it was a very unsatisfying way to learn vi.
My brain is most receptive to learning when it knows the underlying philosophy of why things are designed the way they are. Previous comment with some links.[0]
Once one knows the design intentions behind vi, the learning feels much less random.