My houseplants keep dying. Diagnose me.

Same window, same watering schedule, same optimism every single time — and somehow the plant still dies within a month. Overwatering kills more houseplants than underwatering, but so does the wrong light, root-bound pots, and just plain bad luck with a plant that was struggling before it even reached you. Bring your unkillable recommendations and your worst failures — what's actually survived on your windowsill, and what have you buried?