Backwash Causes Lift?

Le Chaud Lapin writes:

By the bottom part of the wing, right?

Any displacement of mass downward will produce a matching upward forced. You
could generate lift of a sort by launching rocks off the wing, but you'd soon
run out of rocks so that's not very practical. But there's plenty of air
mass, so if you can find a way to divert it, you can generate lift.

If you have compression under a wing do to extended flaps and laminar
friction of airflow, for example, then the lower surface of the wing
forces air downward, and the air beneath the lower surface forces wing
upward.

In reality, the high pressure effects below the airfoil are almost
insignificant. The lift is generated mostly by the diversion of air flowing
over the wing downward.

Why is this all so important?