Prior research demonstrates a willingness to incur costs to punish norm violators. But, how strong are the motives underlying such acts? Will people rely on "excuses" to avoid acting on costly punishment intentions, as with other costly pro-social acts? In a laboratory experiment, we find that third parties punish reluctantly: they state a preference to punish, but avoid the opportunity when doing so does not reveal this as their preference. In contrast, second parties - those directly wronged - are resolute punishers: they actively seek out the opportunity to punish. Our findings highlight important differences in motives underlying second- and third-party punishment.