If you turn the key too long, you can burn up the starter. You also run down the battery, which will require a jump start.

If you just turn the key and nothing happens, do not continue to hold the key in the "start" position. If you held your breath for 25 seconds would you be dead? Maybe not, but if you did it for 30 seconds, 60 seconds, or longer, you could die from lack of oxygen to your brain.

The same could happen to your car's starter motor. Holding the key in the "start" position will cause it to draw more and more current from the battery. Eventually it can draw so much that it causes a high enough resistance in the circuit that it causes either a fuse to blow or a wire to melt or catch fire.