The rule: whatever action the product exists to make habitual is the action a limit must never interrupt. For us that is writing something down.
This sounds obvious and it is violated constantly, because the core action is also usually the one that generates cost, so it is the natural place to put a meter. The damage is asymmetric and delayed: a user who hits a wall while doing the thing you spent months persuading them to do does not upgrade, they stop, and they stop having formed exactly the wrong habit. You have spent acquisition budget teaching someone that the product says no.
Practically this means limits attach to accumulation, never to the individual act — a total, not a rate; a ceiling reached over months, not a counter that resets and blocks you on a Tuesday. And it means that when the ceiling is hit, the message is about the total and offers a way to reduce it, rather than being a refusal attached to the thing the user was in the middle of doing.
Where the money comes from instead is a separate question, deliberately answered separately and later, so that the answer never gets to reach back and put a toll on this action.