“We often hear people indignantly asking others, “Don’t you know who I am?” But if, instead, we could just ask ourselves, “Do I know who I am?” and perform sincere self-inquiry, we could find a permanent solution to all of life’s problems. Tragically, our approach to education is lopsided. We spend our entire lives trying to learn everything about the external world and the lives of other people, yet we never try to learn about ourselves, the inner world.”

These statements have been misattributed to Mandela, as being in his inaugural speech of 10 May 1994 http://www.wsu.edu:8080/~wldciv/world_civ_reader/world_civ_reader_2/mandela.html but this is not the case. Rather, they originate with author Marianne Williamson.
Misattributed

Source: A Return to Love: Reflections on the Principles of "A Course in Miracles" (1992), Ch. 7 : Work, §3 : Personal Power, p. 190 (p. 165 in some editions). This famous passage from her book is very often erroneously attributed to Nelson Mandela. About the mis-attribution Williamson said, "Several years ago, this paragraph from A Return to Love began popping up everywhere, attributed to Nelson Mandela's 1994 inaugural address. As honored as I would be had President Mandela quoted my words, indeed he did not. I have no idea where that story came from, but I am gratified that the paragraph has come to mean so much to so many people."

Variant which appears in the film Coach Carter (2005): "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. Your playing small does not serve the world. There is nothing enlightened about shrinking so that other people won't feel insecure around you. We are all meant to shine as children do. It's not just in some of us; it is in everyone. And as we let our own lights shine, we unconsciously give other people permission to do the same. As we are liberated from our own fear, our presence automatically liberates others."

Variant which appears in the film Akeelah and the Bee (2006), displayed in a picture frame on the wall, attributing it to Mandela: "Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. We ask ourselves, Who am I to be brilliant, gorgeous, talented, fabulous? Actually, who are you not to be? We were born to make manifest the glory of God that is within us. And as we let our own light shine, we unconsciously give other people permission to do the same."

The grand old man of American psychiatry on what he has learnt about life (and death) in his still-flourishing career, The Independent http://www.independent.co.uk/news/people/profiles/irvin-d-yalom-interview-the-grand-old-man-of-american-psychiatry-on-what-he-has-learnt-about-life-10134092.html

Quotes from Words of Wisdoms Vol.2

On how women should embrace their true selves in “Lena Waithe's Message to Women: 'Stop Giving a S--- What Other People Think'” https://variety.com/video/lena-waithe-message-to-women-variety-cover-shoot/ in Variety Magazine

Hayward, California, USA, March 1, 1985
1980s

Source: Collapse: How Societies Choose to Fail or Succeed (2005), Chapter "The world as a polder: what does it all mean to us today?", section "Reasons for hope" (Penguin Books, 2011, page 521, .