This is one of my favorite quotes. The truth is that we are far more capable than we know.
Often we are told quite the opposite: Did you ever have a teacher who told you that you were stupid? Did you ever have a "friend" who would make "jokes" at your every mistake? Did you ever see an ad that told you there was something wrong with you and that you needed the latest money making drug to enable you to live with it?
All around there are attempts to tell us that we are incapable and that we need someone or something in order to survive.
Well, the truth is in the quote above. Start believing in yourself. A potentiality is an ability that may be developed, so even though you may not see your abilities right now, they are there and you can develop them.
Don't listen to the naysayers. You have great potential abilities and there are many ways to develop them. Education is a real good one. The one I recommend is Scientology, because it has worked so well for me.