The logic behind cure and prevention is very simple and it is all about timing: whatever issue we find AFTER running the application will be considered as a situation that needs a cure. On the other side, the very next time that we use that solution BEFORE the issue arises then we consider it as prevention. So technically what we call a cure here is a note that mentions something is broken and it needs our attention. It simply informs us about it and does not patch it up by itself.
Tip
Please keep in mind that there are situations where we cannot find problems until after code execution. For example, we cannot find out if the query result is valid and is within the acceptable range, without letting the Google CSE (Custom Search Engine) do its job. So what happens at that point onward - technically- is a cure, not prevention.
That means we cannot save the query quota before trying something. However, we can save the Firebase quota and database space...