Same thing that has already been stated.

A jet engine sucks in air and pushes it out. So it is pulling itself through the air. Kinda like you pulling yourself with a rope, you pull the rope in and go past it. Now think of yourself in an Indiana Jones or DougB movie in one of those mining carts. And they had a large 2 3/4 DBN rope attached to the wall 600ft in front of you and 22ft behind you. If you pull yourself you will go forward correct? The track is level. Now if the track suddenly started moving like a in the opposite direction and the wheels started spinning and you just held on to the rope, the cart will just stay there right. Now start pulling yourself, it does not matter how fast the track is moving against you, you will still pull yourself forward. Same thing the plane does, it pulls itself through the air, unless one of the frictionless bearings was not repacked lately or got water in the hub or forgot to put it in 4x2 mode, the ground would not have say in which way the plane travels. Get it?

I just want to tell you both good luck, and we're all counting on you.