Positive affect and the activity of the neurotransmitter dopamine seem to shift the balance between cognitive flexibility vs stability towards increased flexibility. Here we examined the impact of prospective monetary gains on this balance. Seventy healthy volunteers performed a set-shifting task comprising a condition in which a bias towards new stimuli helped to overcome perseveration and increased flexibility, and a second condition in which directing attention towards new stimuli increased distractibility. From previous studies of executive functions, two contrasting predictions can be derived: the prospect of monetary gains might either increase cognitive flexibility due to a dopamine release in the prefrontal cortex or increase stability due to an assessment of high utility of action processed in the anterior cingulated cortex and orbitofrontal cortex. Overall, we observed increased cognitive stability in the face of prospective gains (η2 = 7%). However, this effect was modulated by the subjective evaluation of the reward cues: participants who reported increasing their effort in response to reward cues showed increased cognitive stability, whereas those who reported a positive and relaxed attitude towards the reward cues showed increased flexibility (η2 = 11%). The results thus suggest that the flexibility–stability balance is modulated by the perceived effort needed to receive the potential reward. On a neuropsychological level, an interaction of dopaminergic and noradrenergic processes might be involved in the allocation of control.