There are only 21 women who head up Fortune 500 companies. Deanna Mulligan is one of them. For the past five years she has been the CEO of Guardian Life Insurance of America, which is ranked number 226 on the Fortune 500.

She tells Fortune’s Susie Gharib that her path to the top was “unorthodox.” She left a high-powered job at McKinsey shortly after being named partner to work with one of her clients. She also took time off to deal with a family emergency and then started her own consulting company before joining Guardian. “Nobody would look at that and say, ‘okay here’s a prescription to become a CEO’”, she says, laughing. “But it worked for me.”

Why did it work? “I was always doing something I found fascinating, where I thought I could make a difference and help other people and I was truly passionate about it,” Mulligan explains. The mistake many women make, she says, is that they feel obligated to “check this box and this box and this box” so they can follow a prescribed path to the top.

She expects more women will move into CEO jobs in big companies, especially now that there’s “a great pipeline of women” coming into business equipped with MBAs and law degrees. Her advice to women aspiring for those top jobs: “Trust your own judgment. Trust instinct. Trust your gut.”