Neal Roese, If Only:

"A key restriction on the plot counterfactual is the degree of variation, or the amount of alteration to reality, that should be used for maximum entertainment. In a nutshell, there must be recognizable alteration, but it must not be too extreme. You might call this a basic law of art, and I’ll call it Berlyne’s Law in celebration of the psychologist Daniel Berlyne, who several decades ago first applied the tools of experimental psychology to an understanding of how art influences emotion. His insight was to demonstrate experimentally that what strikes us as good art is usually a slight deviation from our expectations. Art that perfectly fits our expectations is boring (been there, done that); art that is too large a departure from what we already know strikes us as bizarre and repugnant (too “out there”). Somewhere in between the extremes of the boring and the bizarre lays a sweet zone of recognition coupled with mild surprise. What most people, on average, consider to be great art more often than not represents a modest (but not large) change from the status quo.

Berlyne’s Law applies to counterfactuals as well, whether they are used by artists to influence an audience’s emotions or as persuasive arguments to convince someone of a particular point of view. A persuasively compelling counterfactual, one that convinces you that some alternative might well have happened, must follow what Phil Tetlock has termed a minimal rewrite rule. Small, minor changes to reality are fine; big changes leave the audience baffled."