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always jumping to one side or the other. For example, if the kicker chose

his good side 65% of the time instead of 59.7%, he would make only 72.6%

of his shots against a goalie who exploited his strategy by always jumping

at his good side.

The key to mixed Nash equilibria is that in equilibrium, each possible

move has an equal payoff.

When playing the equilibrium strategy, on any given shot, the kicker

expects a 74.0% chance of a goal regardless of which side he kicks on. If

he expected a better chance on either side, the goalie would respond more

often to that side, pushing down his success rate there. This equal-payoffs

property is a useful intuitive way of thinking about equilibrium strategies

without using math. Just look for the proportions where each option leads

to the same average payoff.

Can players actually do this kind of numerical analysis? No, but aver-

aged over many players, people are incredibly good at intuitively finding

optimally mixed strategies. Studies on real-life kicking percentages reveal

that kickers as a whole kick on their good side with almost exactly the

correct frequency.

So is that it? We simply count the payoffs, work out the mixed strategy

percentages, and let players flip their weighted coins? Thankfully, no—in

real games, game theory interactions are only a foundation for a fuzzier,

more psychological, more human type of interaction called
yomi
.

Yomi

YOMI is the mind game of predicting, deceiving, and outwitting an

opponent to get advantages outside the game theory math.

I'm borrowing the term
yomi
from fighting game designer David Sirlin,

who borrowed it from the Japanese word for
reading
(as in reading the

mind of the opponent). Flipping weighted coins isn't interesting, but

trying to read a person's mind is. That's why design patterns like rock-

paper-scissors and matching pennies are only a skeleton of a game. The

emotional value of the game grows from the yomi flesh around that

skeleton—from making your opponent think you'll use one move so that

you can counter with another, or letting him think he has tricked you

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