Murphy's Law of Engine-Idling Duration
"If you leave your vehicle's engine running during a delay in proceeding (traffic-jam, road construction, accident-resolution, "stuck" red signal-light, etc.), you will be sitting there for many minutes, just wasting gas. The instant you turn the key off and climb out of your seat to stretch, however, THAT'S when the line of traffic will begin moving again, and thus you will have shut off your engine "for nothing", AND you will now be holding up everyone behind you while you hastily hop back into the driver's seat and re-start the engine so that you can move forward again."
I finally took da plunge and bought a second-hand Toyota Prius because I'd eventually had one too many cases of Murphy's Law of Engine-Idling Duration... the Prius automatically shuts down its power during stand-stills, and then uses its electric motor to provide instant mobility as soon as you're ready to go again.