I spend way too much time thinking about might-have-beens. For example, I am moderately obsessed with the idea of infinite parallel universes. This usually comes up in the context of a near miss with serious injury. Every time I nearly get run over because I am crossing the street and reading a book at the same time, I think about the Amber1 who was hit by the truck and the Amber2 who was only glanced and so on.
Ditto absurd hypotheticals. Which documents from the library of Alexandria would you save? Which historical personages would you clone? Which altered event in Russian history would have maximum impact on the present? Etc.
Is this just me?