Seneca isn't simply saying worry makes you sad—he's identifying something more subtle: anxiety doesn't actually address the future, it only poisons the present moment, which is the only time you're ever actually alive. A parent lying awake at 3 a.m. fretting about their child's job prospects isn't protecting anyone; they're only stealing their own sleep and leaving themselves depleted for the real challenges that arrive tomorrow. The Roman Stoics understood that misery comes not from difficulty itself but from the mind's habit of rehearsing catastrophes that may never occur, turning imagination into a kind of self-inflicted torture.