This work aims to present the role of Doubt and Certainty in our actual and theoretical activities, based upon Ludwig Wittgenstein's On Certainty. In order to do that I first show that real doubt makes sense in light of its actual effects; then, 1compare Wiltgenstein's view with that of Peirce, for whom doubt arises from surprise and moves us to action. Finally, I finish stressing the permanent movement between doubt and certainty as belonging to We itself.