The forthcoming film Molly’s Game, which stars Jessica Chastain and arrives in theaters on Christmas Day, takes moviegoers on a high-stakes trip through the world of underground poker. The story, about a world-class skier named Molly Bloom who went on to run the world’s most exclusive high-stakes poker game (only to become an FBI target), represents famed screenwriter Aaron Sorkin’s directorial debut.

Better still, it’s all true.

The real-life Bloom took the stage at Fortune’s Most Powerful Women Next Gen Summit in Laguna Niguel, Calif. to share to a room full of entrepreneurial businesswomen some of the lessons she learned running a decidedly different kind of startup and, well, getting a bit far over her skis.

“The motivations I had for being successful were somewhat dysfunctional,” she told Fortune’s Pattie Sellers. Bloom is a member of a family of high achievers—one brother is a two-time Olympian, the other is a Harvard surgeon. The bar was high for her to succeed. “Literally if you weren’t the best in the world in my family, it wasn’t impressive,” she said. “I was looking for this thing that was going to make me feel fulfilled inside.”

So she built one of the biggest and most exclusive poker games in the world—one that included clientele like Hollywood actors Leonardo DiCaprio, Tobey Maguire, and Ben Affleck. One regular game in New York had a $250,000 buy-in, attracting Wall Street financiers and leading to evenings where people would win or lose millions of dollars in one session.

“I finally had that thing,” she said. “And I think that’s what led to the compulsiveness to chasing it so far down the line.”

[youtube https://www.youtube.com/watch?v=Vu4UPet8Nyc?rel=0]

The trick to Bloom’s business? Being the bank, rather than another player. “I was bankrolling the games, vetting the players, extending the credit,” she said. “My life was really stressful. I didn’t have the traditional resource to collect on debts and I’m certainly not going to be violent about it.”

Better still, she paid taxes on her underground business. “In 2009, my tax returns showed over $4 million,” she said—not from the game itself so much as the lucrative tips for extending credit to players. “Sometimes those tips were really big,” she said. “One night, I saw someone lose $100 million.” Someone had to guarantee the money—and that someone was Bloom.

The venture soon turned for the worse. Customers came to include men from the Russian mob. She was stiffed money often. She became addicted to drugs. And in the last seven to eight months of her career running games, she took a percentage of the pot. “That’s where I crossed that little gray line,” Bloom acknowledged.

Was it ambition, greed, or naïvité that did her in? “I think it was all those things,” she acknowledged. “I was in way too deep…trying to hang onto this thing that had established and legitimized me.”

The silver lining: Bloom’s role as the bank helped her learn to value herself as a potent businesswoman in her own right.

“I was no longer this object of desire,” she said. “I was someone who let them have their money to play the game—or didn’t.”