The paper deals with the ethical-moral dimension of Popper’s critical rationalism, which is the less analyzed aspect of his philosophy. Critical rationalism is not without assumptions. As a life attitude, it is actualized on the basis of one’s moral preferences based rather on assumptions than on critical reasonableness. Critical rationalism does not exclude logical argumentation and reasoning, but the adoption of them is predominantly the result of an individual moral decision and choice, based, paradoxically enough, on an irrational belief in reason. The author considers this attitude to be productive, as it emphasizes individual moral responsibility. Nobody is able to persuade us about the relevance of what we don’t want to adopt and apply. Thus we find ourselves in the sphere of personal morality.