Most prominently since Plato’s quest for truth (ἀλήθεια) instead of appearance (δόξα), the human race is driven and defined by its urge for knowledge. Our mental capacity is the unique feature that sets us apart from the animal world according to Aristotle and Cicero. Animals do also have knowledge, but apart from also learning through experience, humans intellectually form (a priori), argue and justify beliefs in order to maintain justified true beliefs in an epistemically rational way. This essay aims to answer the question how we can know anything by first challenging the objections of radical skepticism, secondly by analyzing a priori knowledge and finally by stating that epistemic rationality is instrumentally valuable, indispensable and prudent for getting humanly attainable knowledge.