"I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all." Ecclesiastes 9:11

Introduction

Luck plays a significant part in many games. Indeed, some games, such as snakes and ladders, are entirely a matter of chance yet still manage to captivate their players.

One of the many decisions, therefore, that the designer of any game must make is whether or not to add an element of luck in the form of probability-based randomness.

Chance outcomes clearly do not always improve gameplay, but nor do they always necessarily hinder it.

In some circumstances, luck enriches the very forces that motivate players, whilst in other circumstances it does the exact opposite.

The nature of luck, however, is not always self-evident as the following well-known and enigmatic aphorism of Stanislaw Jerzy Lec illustrates.

"If a man who cannot count finds a four-leaf clover, is he lucky?" Unkempt thoughts (1962)

Game developers are sometimes faced with similarly challenging decisions when contemplating whether to include some kind of deliberate randomness. For example, in the video game Unreal Tournament, when a player shoots at a target with the "enforcer" weapon, the projectile does not necessarily hit the point that is aimed at; a random deviation is added that scatters shots.

This introduces a degree of realism from an observer's perspective and no doubt gives beginners a fair chance against more experienced players, but it can also potentially frustrate skilled players.

Is it overall a good idea and, if not, could realism have been introduced in a better way?

Here in this article, with particular reference to computer games, we present a formalism through which designers across all genres and platforms may better understand not only the nature of luck, but also the effect that it has on gameplay and player motivation.

We show that luck is easily broken down into individual categories and that in doing so, a positive or negative effect on particular aspects of gameplay is observed.

First we investigate and classify the various types of luck that occur. Next we enumerate various qualities of gameplay such as motivation and learnability. We then relate the types of luck to their effects, good or bad, on these qualities.

The designer of a new game examines each proposed probabilistic feature and determines which types of luck it produces within the taxonomy. The influence of the proposed feature on each of the various qualities of gameplay is then readily calculated.