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November 7, 2016 10:03 AM EST

Since audiences met Cameron Diaz in 1994 in her debut feature film, The Mask, she has always been known as the confident girl-next-door with bombshell looks and a sense of humor. Though Diaz, 44, does have that confidence as an actress, her success in film didn’t automatically translate to confidence as an author — at least according to her before she released The Body Book: Feed, Move, Understand and Love Your Amazing Body in 2013.

“Right before the book came out, I was on my back for a week. My back went out. I couldn’t breathe,” she told the audience at sister in-law Nicole Richie‘s Pearl xChange at The London in West Hollywood, California.

“I’ve never had that kind of thing where I was just literally debilitated. I realized I was just so scared that I was going to put this thing into the world and everybody’s going to see me, and what if they don’t like me? What if they think I’m crazy or I’m stupid? I was like, oh God, this is so painful,” she shared.

She dug deeper into her insecurities about releasing the book and shared them with the audience. “It was revealing about who I was. Movies are like totally fake. It’s not me at all. It is, but they’re characters. This book was all me. There was no hiding. I was so open and so raw,” she explained.

Turns out, plenty of people liked the raw and vulnerable Diaz. The book became a New York Times bestseller, reaching No. 2 in March of 2014. For Diaz, that gave her the confidence to write her second book, The Longevity Book: the Science of Aging, the Biology of Strength, and the Privilege of Time, released in June 2016.

Regardless of the commercial success her books have received, Diaz insists that does not define true success for her. “Success is really not about what somebody else says. Being a New York Times bestseller, to me, that’s not the success of the book. The book isn’t the numbers that got sold. It was that I had an intention, and the intention was to get that information out to as many women as I could.”

She continued by advising the members of the audience to forget material possessions and to look within to define success for themselves.

“You have to forget about what success is to everybody else, and you have to know what success is to you,” she said. “You have to know that it’s not about how much money you make, or what car you drive, or what bag you buy, or how many likes you get. It’s all about your intention of what you want to accomplish on a personal level.”

This article originally appeared on People.com

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