  Evolutionary game theory has proven to be an elegant framework providing many
fruitful insights in population dynamics and human behaviour. Here, we focus on
the aspect of behavioural plasticity and its effect on the evolution of
populations. We consider games with only two strategies in both well-mixed
infinite and finite populations settings. We assume that individuals might
exhibit behavioural plasticity referred to as incompetence of players. We study
the effect of such heterogeneity on the outcome of local interactions and,
ultimately, on global competition. For instance, a strategy that was dominated
before can become desirable from the selection perspective when behavioural
plasticity is taken into account. Furthermore, it can ease conditions for a
successful fixation in infinite populations' invasions. We demonstrate our
findings on the examples of Prisoners' Dilemma and Snowdrift game, where we
define conditions under which cooperation can be promoted.
