I’ll miss Peggy Olson. For me, Mad Men was all about Peggy’s remarkable career ascent from her first day in her new job as Don Draper’s secretary to ultimately becoming a highly respected Copy Chief.

Along the way, Peggy made some great career moves (such leaving the agency as an undervalued copywriter, and later returning as Copy Chief) and some truly awful ones (such as awkwardly making a pass at her boss on her first day at work, and getting romantically involved with more than one married coworker.)

But here’s one of my favorite Peggy moments.

In the final episode of season three, Sterling Cooper’s corporate overlords in London are preparing to sell the firm. Roger, Bert, Don and Lane have hatched a plan to go rogue and become partners in their own agency, but a mountain of paperwork stands in their way. So Roger, Joan and Peggy are working late into the night, to get the client and accounting files in order.

Roger announces that he’s tired. “Peggy, can you get me some coffee?” he asks.

To which Peggy replies “No,” without hesitation, explanation or defensiveness—just a simple “no.”

It’s a perfect reminder that “no” can be (and sometimes should be) a complete sentence.