Have you ever wanted an Assassin's Creed game that had multiplayer co-op for the game's single-player? If you're one of the few that said yes, you almost got your wish back when the first game in the series got released.
In an interview with OXM, Assassin's Creed 3 mission director Philippe Bergeron revealed that the the first game in the series was originally set to include this feature, but they decided against it since it "didn't fit."
Before we knew about the Desmond story and Animus link, we had a huge co-op component in there…But it just became too hard to do: the engine couldn't support it, and then the metaphor we had above it didn't support it. Co-op was one of those big things at the beginning that just didn't make sense in the end,
Bergeron goes into detail on why he thinks co-op wouldn't work, especially since you played most of the game as Desmod's ancestor.
There was no way to reconcile having multiplayer or co-op in an ancestor's memories. Your ancestor lived his life in a certain way, so assuming you had branching storylines, it creates a paradox. It didn't fit.
While the franchise never did implement a single-player co-op experience — at least not yet, it did venture into mulitplayer territory but with a competitive twist back when it released Assassin's Creed: Brotherhood.
Would you have wanted to see a co-op mode in an Assassin's Creed game's single-player affair?