The Mad Men creator on the season finale, Joan's big decision, and how Pete Campbell takes a punch.

Slate: Exactly—the Campbells seemed battle-tested. So what’s come over Pete? Is it just those Cos Cob groundhogs and long train rides getting to him?

Weiner: I think that’s a lot of it. I think a lot of it is him aging. And a lot of it is him switching places with Don. In fact, that shot at the beginning of the season where we’re coming down the train—it’s the way we always introduce Don. But there Pete is, on that train. This is a guy who has professed his love, attachment, etc. for Manhattan—we know that it is his whole identity.

Slate: How did you settle on the idea of having Pete get punched not once but twice this season?

Weiner: We actually were talking about him getting off the train and getting in a road rage incident. But we really wanted him to get hit a couple of times on his way home because he was having such a bad day. It was an expression of his frustration—though not that he wanted to be punished. And anyone who has been on that train knows that conductor.

Slate: I’ve been on that train; I think I know that conductor.

Weiner: The actor was great. He knew that conductor, too.

This interview has been edited and condensed.