It's a failure of our internal simulatory abilities. People are usually much more confident in their counterfactual beliefs than they have any right to be. Self reinforced internal narratives ("if only this had happened then this would have happened") seem necessary in order for us to maintain confidence in our predictive abilities. I wonder if we were truly aware of the surrounding cloud of possible alternative outcomes, if it'd be paralyzing for otherwise mundane activities. How many times do we escape death by the thinnest margins everyday, without ever being the wiser.