Luck. The mechanic that players can’t really control, where results aren’t determined by players’ actions but by chance, most commonly by rolling dice.
Luck gives power to systems rather than players. And varying the amount of luck can change games.
Let’s take two classic examples: Chess, and Snakes and Ladders. There’s no luck in Chess: every move is completely controlled. On the other hand, Snakes and Ladders has 100% luck: the player makes no choices.
Do you see something about luck here? Chess takes forever, while Snakes and Ladders usually ends in minutes. Yes, luck usually shortens and simplifies games. How? By removing options. Instead of a set of decisions, designers can shorten games by replacing a several with one action: roll a die and use the result.
Part of the reason why games with luck are shorter is because there are fewer decisions to make. Of course, the other reason is that when luck is involved, players tend to spend less time analysing, since even the best made plans can be ruined by bad rolls. (Or really, players aren’t worried about analysing since they can blame failure on the dice.)
Another good thing about luck is that it levels the playing field. Players who are behind have a possibility of catching up. I’m not suggesting that people base their entire strategy (or game design) on luck. What I am saying is that luck can help break ties, or give one player just enough edge over the other to win.
What I’ve discussed is really just scratching the surface of luck. After all, there’s still different types of luck: that is to say, how designers incorporate luck into their games. But that’s for next time.