You have to pass your exams before you go to the next level.
Think about it,... in school you need to pass your exams before you go to the next level. You are given information and you need to learn the information that was presented to you.
What happens when you get an "F"?...Remember when you studied for a test and you failed? or got a really low score? maybe you didn't even studied at all... The main point is that the information was presented to you in class and maybe you were given time to learn it. The moment you received your test score and you received an unsatisfactory score, it usually means one thing... it means you haven't learned the lesson/information.
Now in the school of life, when you pick up a book or listened to a personal development information, simple enough, it is easy to understrand and you know you got the grasp of the information that was presented to you. Remember when you studied and you even believe in your core self that you understood the information. Exam time arrived and you got a "D+"... What the heck just happened!? Hey,... you were sure you answered the questions right,... you were even 100% sure you'll bet your lunch money that the answer was 'C' and not A, B, D, or E.
So my question to everyone is...
How do you know that you have learned the lessons in personal development informations when you didn't undergo an exam or test and be graded to your level of competency/understanding?
Remember the school's experiments? yeah, they were fun and exciting, I loved them too. So now you have listened to a personal development information or read a book. What experiments did you perform? Did you try and test the information out? Did you succeed in the experiment? Did you learn anything?... Of course you've learned something!...
"I've learned my lessons, I won't do it again!" Proclaiming you've learned something is an empty conviction. Your actions reflects what truths you possess inside 
I think that's
the missing key in personal development. You need to find a way to test yourself unbiasedly and grade yourself to find out if you have learned something at all... whether it went in one ear and then out the other.
