There's a tidy framework going around for idle game economy design. Three sinks — Progression, Engagement, Prestige — and for each one, a row telling you what it absorbs: permanent upgrades, refills and boosts, cosmetic items. Good starting map. But "absorbs" is doing something sneaky, and if you don't catch it you'll mis-tune every economy you touch. A sink, by definition, destroys a resource. It's the opposite of a source, which mints resources into the economy. So when a framework says a sink