  We investigate the fluctuations induced by irrationality in simple games with
a large number of competing players. We show that Nash equilibria in such games
are ``weakly'' stable: irrationality propagates and amplifies through players'
interactions so that huge fluctuations can results from a small amount of
irrationality. In the presence of multiple Nash equilibria, our statistical
approach allows to establish which is the globally stable equilibrium. However
characteristic times to reach this state can be very large.

Condensed Matter