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Mary-Kate and Ashley Olsen have been showing us what it means to be a #girlboss pretty much since birth, so it came as no surprise when the entrepreneurial pair offered some work-related words of wisdom in a recent interview.

Asked by Lauren Eggertsen of WhoWhatWear to “give five words of advice (or less) to female entrepreneurs,” Mary-Kate said simply:

“No is a full sentence.”

What makes this advice so powerful? Research has shown that women are more likely than men to say “yes” to extra tasks at work, which can hold you back from being promoted. Taking on too many extra tasks leaves less time to complete your actual job, so your opportunities for advancement can become limited. Plus, women tend to feel more guilt than men about saying “no” to a work-related favor—a byproduct of social norms that teach women to be cooperative nurturers.

Don’t beat yourself up if you’ve been in this situation, though. Even actress Lena Dunham was once a “yes” woman, always agreeing to extra work and putting herself last on her list of priorities.

In an essay on LinkedIn earlier this year, she wrote, “At work it became my mission to answer every email no matter the hour, agree to every added task, finish the day off by reading a link sent by a colleague rather than a book for pleasure.”

But constant people-pleasing eventually wore her down, and during the third season of Girls she finally felt a shift.

“It was a slow process, but a polite ‘no’ soon entered my vernacular. ‘I can’t do it realistically by Friday,’ or ‘I wish I could be on that panel but my week is insane,’ or even ‘No, I’m not comfortable with this dynamic.'”

While saying “no” to extra work can, in some cases, have a negative impact on your reputation, it will help you in the long run. Susan Newman, a psychologist and author of The Book of No, suggests that women establish clear boundaries at work and be “brief” and “bright,” and then “be gone,” when saying “no” to an extra task. We think the Olsens would agree!

What’s the best career advice you’ve ever received?