Sorry for the poor joke.
What exactly causes a toilet to run, and why or how does “jiggling” the handle alleviate the problem? Is there a more permanent fix? My toilet seems to run at various points in time, and it’s becoming bothersome. Does a running toilet waste a significant amount of water, if any?
It’s the flush valve on the bottom of the tank not seating properly. Replace it, they’re cheap enough.
Wow, that was fast! Thanks a bunch.
That is the most common reason, but I’ll offer another one if that doesn’t work. When the handle is released, but the valve is still floating open, the chain goes slack. If it’s a poorly designed chain it can tangle, and then not straighten out afterwards.
I suppose the solution in this case is a new chain. I really should get around to it. 
But your problem is still probably the valve there.
Actually, its like a big black rubber plug that you have to put a new one on now & then, so it seals right. Best to bring it in to match it up with another one as they aren’t the same & then you can get a chain too. You’d probably want to turn the water off to the tank first.
Open the top of the tank and watch what happens while you flush. There are any number of things in there that can make the toilet ‘run’.
When you flush, the contents of the toilet bowl go down the drain, and a drain is opened in the tank so that the fresh water in the tank can go into the bowl. When all the fresh water has drained into the bowl, the drain closes and the tank starts to refill with fresh water. That’s the hissing sound you hear for a minute or so after you flush.
When the water level gets high enough, there’s a float in there that gets pushed up by the top of the water. The drain closes and the fresh water stops refilling the tank.
If your toilet is ‘running’, something is stopping the drain from closing, so the water that comes into the tank just goes right back out into the bowl and keeps going on through, so you waste a lot of fresh water. The seal around the tank drain might be bad, or the chain that connects the flush handle to the drain might have gotten tangled or stuck under the seal. Unless it’s a faulty part like a bad seal, jiggling the handle or lifting the hood and manually straightening things out (which is safe because the water in the tank is as clean as the water from your sink faucet) does the trick.
I’d definitely get right on this. I did the ol’ jiggle-the-handle bit for a month or so, even bending the float arm and thinking myself pretty clever, until, one night, the thing just went berserk and kept running at maximum force. The plumber put in some newfangled contraption that doesn’t even involve a float (he said those wre old school) and works perfectly.
As Cat Fight mentions, bending the float arm down can work, if the running is consistent. Sometimes the float can leak a bit and sink deeper than it should. That lets the arm stay too low, so the water doesn’t turn off completely and spills out the overflow pipe into the bowl.
From howstuffworks.com’s toilet page. I used this once when my bowl was only partially filling after a flush.