Behavioral extremism (e.g., violent extremism, extreme humanism, or extreme athleticism) elicits fear, revulsion, pity, or admiration depending on the context. Its common image as exotic and esoteric makes extremism fascinating to audiences worldwide. The negative, antisocial and positive, prosocial cases of extremism are generally regarded as poles apart and as based on qualitatively different psychologies. By contrast, we propose that all cases of extremism, across different manifestations and levels of phylogeny, involve the same psychological mechanism. This mechanism consists of a motivational imbalance wherein a given need becomes dominant to the extent of overriding other basic concerns and liberates behaviors that the latter formerly constrained. We discuss the antecedents and consequences of such imbalance and provide empirical evidence to support our claim.