I think the various discussions in these comments show that we don’t realllllly know, just that we understand what forces are there to allow it, and how to generate them.
The fact that the second "we" doesn't really know aerodynamics, and is going to waste man-days chasing its own half-understandings round in circles in the comments, doesn't contradict that fact that the first "we" does understand aerodynamics. Planes aren't staying in the sky by accident, nor even just by the survivorship of trial-and-error engineering.