When Marianne Williamson wrote the words, the professional positive-thinker didn't think they stood out from any of the others in her book, "A Return to Love."

Then someone -- who, exactly, remains a mystery -- incorrectly attributed a 13-sentence paragraph from the book to South African activist Nelson Mandela, turning an inspirational thought into the most famous words she's ever written.

"It's a total urban myth," Williamson said of the idea that Mandela uttered her words, much less included them in his 1994 inauguration speech after he was elected president of South Africa. "I have absolutely no idea how it happened."

Over the years, with help from the Internet, the quote has become so attached to Mandela that even the makers of the new film "Akeelah and the Bee" believed the words to be his, using them in pivotal, inspirational scenes. Although the quote remains in the movie, only a last-minute edit kept out the mistaken attribution.

It all started in 1992. That's the year Williamson shared her thoughts on the 1970s spiritual guide "A Course in Miracles," in her No. 1 best-selling book, "A Return to Love: Reflections on the Principles of A Course in Miracles," a spirituality guide.

At the bottom of page 190, in the 1996 paperback edition, the most famous section of the famous quote begins: "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?"

In "Akeelah and the Bee," which opened last week, an 11-year-old, African-American girl comes to embrace her talent as a speller with the help of a mentor played by Laurence Fishburne. His character uses the quote to help inspire Akeelah toward her quest of becoming a spelling-bee champion.

The film's writer and director, Doug Atchison, added the quote to his script after a filmmaking friend suggested it in the earliest stages of his writing. He was unfamiliar with the passage, so he believed his friend when he attributed the quote to Mandela in an e-mail message.

An edited version of the quote ended up in the script, Atchison said, speaking by phone from Los Angeles. He wrote the script in 1999, and the movie was shot in 2005.

Atchison eventually learned Williamson was behind the quote, but he thought Mandela had at least used it. He planned to refer to Mandela, while also crediting Williamson.

It was, after all, a key theme in the film's storytelling. Akeelah, played by Keke Palmer, at first shied away from competing in spelling bees because she wanted to avoid being teased by her peers. The idea was that Fishburne's character, an academic who teaches Akeelah about W.E.B. DuBois and Frederick Douglass, was going to use the quote to educate her a little about Mandela as well.

Then, about a week before the film's editing deadline, a producer discovered that Mandela never said those words. In the film, Akeelah reads from a framed copy of the passage, which was hanging on the office wall of her mentor. Atchison had to remove a close-up shot that attributed the quote to Mandela.

That a white American woman wrote the passage affects the movie "only in my own little scheme that I wanted to have references to these black thinkers," Atchison said. Mandela isn't mentioned in the movie; Williamson is listed in the credits.

"The intent and content of what the quote is saying is totally valid. It's pertinent to what Akeelah is going through at that very moment, where she's dismissing her own power," Atchison said. The quote scene was often named by test audiences as their favorite part of the film.

The African National Congress, the South African political party with which Mandela is affiliated, is aware that Williamson's quote has been attributed to the former president.

However, "it's not found in any of Mandela's speeches," said ANC spokesman Donovan Cloete, by phone from South Africa. He's not sure how the quote might have been attached to Mandela.

On the phone from her home in Michigan, Williamson says she is humbled that so many people are affected by her words.

"Every writer is hoping that they're going to write something about which someone says 'yes!' or underlines something in yellow. That's why we write -- the hopes of touching someone."

The passage comes from the section of the book on personal power. "I think that it really hits people for the same reason that it hits me and always has. It's an extraordinary concept," she said of the idea -- from "A Course in Miracles" -- that people are afraid of the light in themselves, rather than the dark.

She first heard about the Mandela connection nine or 10 years ago. At first, people were rude to her when she asked them to correct their mistaken attributions. They'd take her to task for attempting to take credit for Mandela's words. Nowadays, people are friendlier about it.

"If Nelson Mandela quoted me, I'd be very honored. I'd be bragging about it all over the place," Williamson said.

She's still curious, however, about the origins of the mistake.

"I've sometimes thought, 'Is there somebody out there who knows?' "