Here's what makes self-made billionaire Oprah Winfrey angry—and how she stays grounded

In a recent interview with InStyle, self-made billionaire Oprah Winfrey reveals what makes her upset these days. Her answer: "What makes me angriest is the lack of discernment," Winfrey said.

To stay grounded, Winfrey relies heavily on advice her late mentor Maya Angelou once gave her, which she also says is one of the greatest lessons she has learned and used throughout her career.

"Maya [Angelou] used to say to me, 'When people show you who they are, believe them the first time.' She said, 'Babe, your problem is you have to be shown 29 times,'" Winfrey told InStyle.

Today, Winfrey sees how this lesson applies not only in her own life but in those of others as well.

"So, I see a lot of people who have to be shown 29 times, who have a lack of discernment for things that appear to be obvious," she told the magazine. "Character is very much a defining matter in everything that you do."

Winfrey also spoke about the subject during a press conference after the Golden Globe Awards in January.

"One of my greatest wisdom teachings is to assess from people's behaviors, their actions — not just towards me but to other people — who they are and how they behave," Winfrey said.

From the time Angelou and Winfrey first got to know each other, Winfrey recalled, the poet and civil rights activist had provided her a solid piece of advice on building relationships with people: Actions speak louder than words.

"When I first met Maya, in the '70s, I couldn't have guessed what the next few decades would bring—or that she would be there for me every step of the way, a wise, loving presence and the greatest mentor I've ever known," Winfrey said.

Winfrey had known Angelou since nearly the start of her career in her 20s and often referred to the poet as her mother, sister, friend and "one of the greatest influences" in her life. In the May 2013 issue of "O, The Oprah Magazine," Winfrey said she had been a fan of Angelou before first meeting in the 1970s. After reading Angelou's award-winning book, "I Know Why the Caged Bird Sings," Winfrey connected to the author's life story.

This is an updated version of a previously published story.