The quote in question, attributed to Nelson Mandela, was written originally by American author Marianne Williamson! My apologies to all, for I too, did NOT know this but relied on other sources. I owe my thanks and enlightenment to "DF" of Massachusetts for providing the actual origin of the quote, not a poem at all, to all of us.
The following was from a website provided by "DF" and explains it better than I can.
This is from The News Observer website, and all rights are reserved by said site:
Often outfitted with semicolons and commas and arranged in poemlike fashion by those who came after her, these words originally appeared in Marianne Williamson's 1992 book, "A Return to Love: Reflections on the Principles of A Course in Miracles."
"As I interpret the Course, 'our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. It is our light, not our darkness, that most frightens us.' We ask ourselves, Who am I to be brilliant, gorgeous, talented, fabulous? Actually, who are you not to be? You are a child of God. Your playing small doesn't serve the world. There's nothing enlightened about shrinking so that other people won't feel insecure around you. We are all meant to shine, as children do. We were born to make manifest the glory of God that is within us. It's not just in some of us; it's in everyone. And as we let our own light shine, we unconsciously give other people permission to do the same. As we're liberated from our own fear, our presence automatically liberates others."