According to director Craig Zobel, Kate Winslet was the only actor confident enough to go back to her native accent in between takes; every other actor was terrified to let it go. For the cast and crew, witnessing Winslet immediately switch from a Delco accent to her normal English accent nonchalantly was an astonishing sound.
Audience viewership increased weekly, due to such positive word-of-mouth. On the evening of the finale, on May 30, 2021, the HBO Max streaming server crashed for several hours for the first time in its history, mere minutes from the episode airing. The finale episode became the most-watched episode in HBO Max history.
Kate Winslet and Julianne Nicholson are friends in real life. Nicholson's husband, Jonathan Cake, is the godfather of Winslet's son, Joe. Winslet recommended Nicholson for the role of Lori, and arranged a meeting to convince her to take the part, assuring her that she would regret it if she didn't accept. Brad Ingelsby knew that the actor that portrayed Lori had to be cast second, given how central the friendship is to the story.
Even though Mare was an athlete in her youth, Kate Winslet didn't want her to be overly fit in her 40s. "I didn't want to make her an impossible, superhuman 40-something-year-old. Most women aren't like that. We do what we can in the midst of the juggle of everything else."
Kate Winslet relished in adding more to the character than what was initially written. She wanted to capture the realness of Mare, and not downplay how exhausted and miserable Mare would be. A lot of her traits, such as her fatigued expression and adding spray cheese to her cheese ball, were added by Winslet on the day. When the director assured her that he could touch up some of her scenes, Winslet outright refused. By her request, the show's poster had to be reworked twice to accurately reflect a middle-aged woman with wrinkles and blemishes. "Faces that change, that move, are beautiful faces, but we've stopped learning how to love those faces because we keep covering them up with filters."