Thought Power could be renamed: The 1,001 ways to say "As you think, so you become" ;-), but the author’s insistence on that one idea actually gives me an incredible insight about what to do next, how to progress on the spiritual path. I must say that until now, my general feeling was that I was a pretty accomplished individual, having excelled in the educational system and being somewhat of a good athlete, i.e., in my words, having "mastered the intellectual and the physical". So it never occurred to me that anything additional was needed, that there really was any way to grow further.
What I realize is that, the same way I have learnt to master my intellectual capabilities in school, and my physical capabilities through exercise, something I need to gain control of (because I can see that I have very little control over it!) is… my thoughts! i.e. what is going on in my head all the time, the little voice in my head saying "this sucks", "I am bored", "this guy is an idiot", "I’m a loser", "Is love fading away?", etc, as I move through life. I realize that, indeed, most of the time I have no control over what is going on in my head! Shattering realization!