The key concepts in the philosophy of Arthur Schopenhauer (1788-1860) connect it to Ancient Stoicism and existentialism. John Vespasian passes review to those concepts, which Schopenhauer first outlined in “The world as will and representation,” a book that he published in 1818. Here is the link to the original article: https://johnvespasian.com/schopenhauers-key-concepts/