“Now I will explain how you can recognize that you are not wise. The wise man is full of joy, cheerful and calm, undisturbed. He lives on equal terms with the gods. Now examine yourself: if you are never sad, if no hope disturbs your mind with anticipation of the future, if by day and night the condition of your spirit is even and unvarying, alert and happy with itself, then you have reached the high point of human good.” Seneca, Letter 59 in Seneca: Selected Letters, trans. Elaine Fantham (Oxford 2010), p. 92.
Seneca’s statement reflects his Stoic philosophy: Temporary emotions do not disturb wise persons, but rather they control their passions through the use of reason. In this manner true happiness (not a temporary mood) rests in the human mind.