I have come up with a better metaphor than “you can’t pour from an empty cup” for burnout. You can’t boil an empty kettle. Pouring from an empty cup just gets you nowhere. Trying to boil an empty kettle can ruin the kettle, the stove, and burn down your house if you keep trying it.
My electric kettle has a “minimum” mark on it. Sometimes I don’t need that much. Every so often, I’ve boiled less water than that minimum, and it hasn’t broken my kettle or burned my house down.
But I really should not do that again.
When it comes to burnout, it’s important to take time to recuperate. To refill the kettle enough, not just some.