That's a great question. It really affected me when i was learning and still does to some extent.
I'm sure it did the same to Paul b/c he tells the story about a seminar where they all activated a book, a complicated book, in a very short time. On the plane back he went thru the entire book and found that they had, in fact, gotten all the key points. <<<< So, that's how to know 
You go back over the whole book & verify what you activated.
That's what i've done countless times. I usually find either none or a couple things i missed. This book on NLP i'm doing right now. I PhR it & marked all the stuff in dry highlighter pencils. It took me no time to do this. As i read it now, i did get all the salient points. I just didn't trust the speed of what i did earlier. I told myself that i really needed to just read this book to get it. Truthfully, i was afraid that i'd missed important stuff.
