What is Seneca's core idea on happiness?
True happiness, as I understand it, resides not in external possessions or fleeting pleasures, but in virtue. A happy life is one lived in accordance with nature and reason, cultivating inner strength and wisdom. It is found in the pursuit of justice, courage, temperance, and prudence, regardless of fortune's favor or disfavor. This inner disposition is impervious to the whims of fate.