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.