That is certainly not a dumb question. Our final reserve fuel is calculated to allow for 30 minutes holding at our alternate (or destination, if that is where we have "diverted" to) at 1,500 feet with our planned payload. Quite rightly, you see fuel as time and/or distance. With 30 minutes fuel at 1,500' we could tip-toe just over 120 nautical miles, at higher levels the same fuel would get you 230 miles or so. The reason for such a short distance at low levels is that jet aircraft are not very efficient there.
Therefore, as you approach the time (but in reality, most of the guys I know would have been thinking this through hours before) when the fuel in your tanks approaches that required for a diversion and 30 minutes, you execute your most sensible Plan B (or C, D etc.). Then this is the point when some (very few) Controllers deal you a card from the bottom of the pack. They may tell you to stay in the hold, or give you a rubbish vector - and that's the point when we call "Mayday". Everyone's attention has been gained and we now insist on a certain course of action. And this is where the sensationalist writing starts.
Good question though.
PM