The anxiety and fear your friend is feeling are real. On occasion, he might also suffer from migraines and violent stomach cramps. However, these too are symptoms that he has created in order to achieve the goal of not going out. YOUTH: That’s not true! No way! That’s too depressing! PHILOSOPHER: No. This is the difference between ‘aetiology’ (the study of causation) and teleology (the study of the purpose of a given phenomenon, rather than its cause). Everything you have been telling me is based in aetiology. As long as we stay in aetiology, we will not take a single step forward.