Oprah says that when she was growing up, reading was her passion -- and she especially loved Maya Angelou's books. "Books were my escape into a world that went beyond my front door," she says in this clip from "Oprah's Lifeclass." "I loved [Maya Angelou's] books. I read I Know Why The Caged Bird Sings I don't know how many times before I was an adult. From the time I opened the first page and [read] 'Whatcha lookin' at me for? Didn't come to stay. Only came to say happy Easter day,' [it] struck me because I was a black girl just like Maya Angelou growing up in the church, being raised by my grandmother, doing Easter pieces."

So it was "unimaginable" to Oprah that as an adult she would become friends with Maya. "Not just friends -- sister-daughter, mentor," she says. "I would now say that she is one of the greatest influences in my entire life. She is like a mother to me, a sister to me, a friend to me."

The very first time Oprah visited Maya, she says her mentor gave her a piece of advice she's taken to heart ever since. "I was telling her my life story and sharing with her some of the mistakes I'd made in my twenties," Oprah says. "And I shall never forget in that moment she said to me, 'That was when you [were] 20. Now you're in your thirties. When you know better, you do better.'"

Oprah says that's one of the "great lessons" of her life, and she shared it on "The Oprah Winfrey Show" as many times as she could (43, to be exact). "You know how freeing those words are? How freeing they can be for you? What it means is you don't have to hold yourself hostage to who you used to be or anything you ever used to do because who has lived and hasn't made mistakes?" Oprah says. "When I think about my twenties and what a foolish girl I was and how I would give over my power to men who really didn't mean me well... But now I hold no grudges against them either because I realize I'm the one who gave over the power because I didn't know any better. And now that I know better I know I don't have to do that again. It's one of the most powerful lessons any of us can ever know."

"Oprah's Lifeclass" airs on OWN.

Click through the slideshow to see some of Maya Angelou's most notable public appearances.

Loading Slideshow...
  • In Honor Of Maya Angelou

    Maya Angelou attends Surprise Oprah! A Farewell Spectacular at the United Center in Chicago.

  • In Honor Of Maya Angelou

    President Barack Obama presents poet and author Maya Angelou with the 2010 Medal of Freedom in the White House.

  • In Honor Of Maya Angelou

    Maya Angelou speaks during the AARP Magazine's 2011 Inspire Awards in Washington, D.C.

  • In Honor Of Maya Angelou

    Dr. Maya Angelou poses at the Special Recognition Event for The Michael Jackson Tribute Portrait in Winston-Salem, North Carolina.

  • In Honor Of Maya Angelou

    Dr. Maya Angelou attends her 82nd birthday at a party with friends and family at her home in Winston-Salem, North Carolina.

  • In Honor Of Maya Angelou

    Dr. Maya Angelou, recipient of the 2009 Buoniconti Fund Humanitarian Award, speaks onstage at the 24th Annual Great Sports Legends Dinner in New York.

  • In Honor Of Maya Angelou

    Dr. Maya Angelou and former U.S. President Bill Clinton attend the 2009 Women of the Year hosted by Glamour Magazine in New York City.

  • In Honor Of Maya Angelou

    Writer Maya Angelou attends the memorial celebration for Odetta at Riverside Church in New York City.

  • In Honor Of Maya Angelou

    Actress/host Niecy Nash and Dr. Maya Angelou attend the 34th Annual AWRT Gracie Awards Gala at the New York Marriott Marquis.

  • In Honor Of Maya Angelou

    Actress Sigourney Weaver and poet Maya Angelou attends the 2009 Straight for Equality awards at the Marriott Marquis.

  • In Honor Of Maya Angelou

    Poet Maya Angelou reads a poem during a ceremony to present Archbishop Desmond Tutu of Cape Town, South Africa with the William J. Fulbright Prize for International Understanding.

  • In Honor Of Maya Angelou

    Hillary Rodham Clinton holds the hand of Dr. Maya Angelou during a conversation in front of an audience at Wake Forest University.

  • In Honor Of Maya Angelou

    Poet Maya Angelou reads her poem 'Amazing Peace' during the 2005 Christmas Pageant of Peace and National Christmas Tree lighting ceremony in Washington, D.C.

  • In Honor Of Maya Angelou

    Dr. Maya Angelou speaks at the Women In Film and Hallmark Channel Reception at the Academy of Motion Picture Arts and Sciences.

  • In Honor Of Maya Angelou

    Coretta Scott-King, who is the widow of slain civil rights leader Martin Luther King Jr., and Maya Angelou speak to members of the media in the Bronx, New York.

  • In Honor Of Maya Angelou

    Maya Angelou laughs at the Abyssian Development Corporation's tenth annual Harlem Renaissance Day of Commitment in New York City.