If you put your hand on the window of a moving car, so that your palm is pointing directly forward, the force?

Question

If you put your hand on the window of a moving car, so that your palm is pointing directly forward, the force on your hand is directly backward. Explain why the two halves of the airstream, passing over and under your hand, don't produce an overall up or down force on your hand?

Answer 1

The two halves of the airstream are balanced, so your hand doesn't move up or down.

Answer 2

Symmetry. But if you tilt your hand, symmetry is lost, the airstream will be deflected upward or downward, and the result is exactly the same sort of lift that enables an airplane to fly.