This riddle asks for something you can spend, save, and waste, yet once it is gone you can never truly buy it back.
The answer is time.
We often use money-related words to talk about time. We “spend” time on work or hobbies, “save” time by doing something more efficiently, and “waste” time when we feel it was used poorly. But unlike money, lost time cannot be purchased again.
That is what makes the riddle so effective. The clue sounds as if it is describing money, but one phrase—“never buy back”—points to something more valuable and irreversible. Once a minute, hour, or day has passed, it is gone. You can use future time differently, but you cannot recover the exact time that has already passed.
