“I thought I was going to be committing career suicide,” the AdCouncil president and CEO says of her fears of coming out in the workplace.

Sherman was out in all other parts of her life: with her family, with her friends—with everyone outside the office. But at her job, she says she pretended that she was straight because she felt it was the best move to protect her career. She even kept a photo of her best friend, Bob, in her office to make it appear that she had a boyfriend.

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Sherman only told her company’s chief executive on her last day working there in 1997. After she did, the CEO took steps to enact benefits for employees in domestic partnerships, no longer limiting benefits to traditional marriage (years before same-sex marriage became legal).

“The lesson for me was you just have to speak your truth,” Sherman says. “And one conversation can make a huge difference.”

The difference was apparent to Sherman in her own life too. “What became very clear, very fast,” she says, “was how much energy it took to hide all of those years.”

In Fortune’s Trailblazer series, powerful women in business share formative stories about overcoming a challenge in their lives. Watch them all here.