According to decades of research in affective neuroscience, the left and right hemispheres are specialized for approach and avoidance motivation, respectively. With the Sword and Shield Hypothesis (SSH) we challenge this conclusion; we propose that the lateralization of motivation depends on the lateralization of motor control for the dominant and non-dominant hands (used preferentially for approach and avoidance actions, respectively). The SSH predicts that the laterality of approach motivation should vary continuously with the laterality of circuits supporting approach-related actions. We measured mood before and after 5 sessions of tDCS applied bilaterally to DLPFC in right- and left-handers. Results in right-handers show that positive emotions increased after left-excitatory stimulation, but decreased after right-excitatory stimulation. In non-right-handers, however, the opposite pattern was found: Positive emotions decreased after left-excitatory stimulation, but increased after right-excitatory stimulation. These results reveal continuous covariation between the neural systems for action and emotion, supporting the SSH.