In order to design games, we need to be able to evaluate whether they will be fun or not. Given a description of a game, it is good to be able to know whether it will work before we create it.

This post addresses a common naive method that is often used for evaulating unproduced game designs. It’s something I call mental simulation, and it’s one of the most basic mistakes in game design.

Mental simulation is the process of imagining yourself playing the game in your head, then evaluating the game based on how that imagined play makes you feel. For example, in evaluating a first-person shooter, one would imagine an intense gun battle in which the player is victorious in some particularly hair-raising way.

Game previews and advertisements are designed to make you do mental simulation. They often describe particular gameplay scenarios in poetic detail. The goal is to make you imagine yourself playing the game and enjoying that experience. This is misleading, because the quality of a possible micro-experience in the game says very little about the quality of the game design as a whole.

The main problem is that mental simulation only allows evaluation of a very short snapshot of gameplay. A person will tend to evaluate the coolest possible moment of gameplay imaginable. This means that the rest of the game is being completely ignored. In almost all cases, the imagined experience cannot be extrapolated to the hours and hours of other gameplay. A game needs to be consistently fun across its entire playtime in order to be effective. Thus mental simulation will make games which are only fun for 5% of their length seem really good, even though the other 95% is very boring.

Mental simulation also fails to take into account learning curve. Since the game is in your head, you understand it fully. This is automatic. Unfortunately, there are countless possible game designs which are incredibly good after the player knows how to play the game well. Evaluating games by mental simulation can obscure the difficulty in learning to play the game.

Mental simulation also tends to produce design ideas that lack rigor and internal consistency. Going from mental simulation to code will almost always reveal gaping holes in game logic which cannot be elegantly reconciled.

There are two cognitive biases that lead people to do mental simulation. The first is that human beings respond very well to narratives. Games, however, are not narratives. They are systems from which a narrative can emerge. In evaluating only one possible narrative, we completely miss the quality of the system producing that narrative.

The second bias is the confirmation bias. This is a problem with the way people test hypotheses. Humans will tend to look for evidence which confirms their hypothesis, when in fact, searching for falsification is much more helpful. In this case, a person using mental simulation is looking for “evidence” for confirm their belief that the game in question will be good. They will almost invariably come up with some idealized scenario, and then extrapolate the resulting emotions across the whole game design. This is not useful.

Instead, try to falsify the game design. Don’t try to think of the coolest scenario possible. Try to think of the most boring scenario possible. Usually you will be able to come up with many examples, because most game designs cannot stand up to this sort of attack. If your design can, you know you have a real gem.

It is almost impossible to avoid doing mental simulation. Just understand that will mislead you if you do it naively.