How long can I keep running on caffeine and willpower?

You already know the answer, because you named it yourself: you are borrowing from a future that will present the bill. Caffeine and willpower are real, but they are loans, not income. They let you keep producing by spending tomorrow's energy today. And loans always come due, usually at the worst possible moment. The reason this feels manageable is that it works, right up until it does not. There is rarely a warning shot. The body absorbs the deficit quietly for a long time and then collapses all at once, in illness, in a wall you cannot push through, in a mistake fatigue made for you. The absence of a crisis so far is not proof you are fine. Start repaying a little now, before the bill is forced on you. Pick one real recovery this week, a full night's sleep, one true day off, and protect it as fiercely as any deadline. You cannot outrun a deficit forever. You can start closing it one honest rest at a time.