Marshall is right of course.

With many of the 617's you only get one chance to start them.

If you let go of the key too soon, and the engine does not continue to run, additional attempts may result in failure.

My theory on this is the fact that there is too much cold wet fuel in the combustion chamber and the cylinder cannot generate enough heat to fire it all off, so, you get nothing. Has happened to me before, as well.

That being said, I do not understand Marshall's suggestion to plant your foot on the floor prior to turning the key. The engine cannot use any more fuel than it can possible burn at idle. Giving it too much fuel, in a valiant attempt to start it, is a recipe for failure, IMHO.