This deep dive focuses on the foundational Greek thinkers of Stoicism, primarily Zeno, Cleanthes, and especially Chrysippus, who are described as the original philosophical engineers of the system. It explains that their original, comprehensive works have been lost, and our knowledge comes from later sources that preserved their intricate arguments. The early Stoic goal was achieving eudaimonia, a state of flourishing or a "good flow of life," which they argued could only be attained through virtue. This virtue was defined as living in accordance with nature, specifically our rational human nature. The episode details the radical Stoic claim that virtue is the only true good, while external things like health, wealth, and reputation are "indifferents". While some indifferents are "preferred," they have no bearing on one's ultimate happiness or moral worth, a stark contrast to Aristotelian thought. This belief is illustrated by the archer analogy: the archer's virtue lies in the perfect execution of their shot, not in whether an external factor like the wind ultimately affects the arrow hitting the target. Chrysippus further developed the system by defining passions like anger and fear as cognitive errors or faulty judgments made by a unified, rational soul. These Greek founders established that the path to tranquility involved correcting these judgments, a process that later became the basis for Roman practical ethics. Their work provided the complete intellectual architecture—physics, logic, and ethics—that later figures like Seneca and Marcus Aurelius would adapt and apply.