  According to the evolutionary game theory principle, a strategy representing
a higher payoff can spread among competitors. But there are cases when a player
consistently overestimates or underestimates her own payoff, which undermines
proper comparison. Interestingly, both underconfident and overconfident
individuals are capable of elevating the cooperation level significantly. While
former players stimulate a local coordination of strategies, the presence of
overconfident individuals enhances the spatial reciprocity mechanism. In both
cases the propagations of competing strategies are influenced in a biased way
resulting in a cooperation supporting environment. These effects are strongly
related to the nonlinear character of invasion probabilities which is a common
and frequently observed feature of microscopic dynamics.
