The trivia items below may give away important plot points.
After the final episode of the series aired, many viewers engaged in fierce debate about the meaning of the episode's final moments. Most interpreted the very ending (in which Don seems to experience a moment of happiness and revelation during a meditation session, and then the real-life 1971 Coca-Cola commercial "Hilltop" plays) to mean that Don realized he was meant to be an adman all along, returned to McCann, and created perhaps the most famous ad of the 1970s based on his experience at the meditation retreat. Proponents of this theory noticed several clues that indicated it, including the fact that Don fixes a Coke machine in a previous episode and also the strong physical and sartorial similarities between many of the other attendees at the retreat and the singers in the ad. However, a significant and vocal minority of viewers and critics believed in other interpretations, including the possibility that Peggy, not Don, created the ad or that the ad did not literally "exist" in the Mad Men characters' lives and instead represented Don's spiritual awakening. These alternate theories were debunked in the days after the last episode aired - first by Jon Hamm (the actor who played Don Draper) in a New York Times interview and then by showrunner Matthew Weiner himself in a public conversation with A. M. Holmes at the New York Public Library. Weiner confirmed that the episode was meant to imply that Don wrote the Coke ad: "The idea that some enlightened state, and not just co-option, might've created something that is very pure [appealed to Weiner]. . . . To me, it's the best ad ever made, and it comes from a very good place."
Jon Hamm claimed that the idea to end the series with the Coke ad was conceived around the production of the fourth season, and it was a long and complicated process to receive permission from the Coca-Cola Company to use their footage.
Joan finally chooses the name "Holloway, Harris" for her new, independent company. Many viewers were left confused about where these names came from. When Joan proposed a partnership to Peggy, she said that their company would be named "Harris, Olson," because "you need two names to make it sound real." Joan also told Peggy that she didn't want a professional partnership with anyone else but Peggy. So after Peggy turned down Joan's offer, Joan gave the company both of her names: Holloway (her original last name from before she was married) and Harris (the name she acquired when she married Dr. Greg Harris and kept even after she divorced him). This verifies the implication from earlier in the episode that Joan has gone into business by herself, with no other partner.