In a powerful Fortune column that went viral Tuesday, the president of an Internet start-up that helps women secure online work is apologizing for the way she treated working mothers in the past.

What changed Katharine Zaleski's mind? The birth of her daughter, Charlotte.

"I’m sorry to all the mothers I used to work with," she wrote in the essay, in which the former manager for The Huffington Post and The Washington Post revealed she regretted the way she'd judged working moms in her 20s.

Listing the behaviors she now feels guilty for, Zaleski admitted she initially dismissed a managing editor's work ethic after surveying the woman's "endless photos of her small children"; didn't protest when "another female editor said we should hurry up and fire another woman before she 'got pregnant'"; and didn't defend a woman who was asked on a job interview how she'd handle the rigors of work and "all your kids at the same time." She added that she would often schedule last-minute meetings at 4:30, without realizing that many working moms might need to pick up their kids at daycare at that time, and viewed staying late at the office as proof she was more dedicated to her career.

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