The lift of a wing in the form of a tilted flat plate with a certain angle of attack can be explained as an effect of
- unsymmetric attachment-separation in real flow (right picture),
which reflects different stability aspects of attachment and separation of symmetric potential flow (left picture) with the flow diverging in attachment and converging in separation. The result is downwash with redirection in real unsymmetric flow, which gives lift as a reaction, while in symmetric potential flow there is no downwash and the lift is zero. Since the downwash is proportional to the angle of attack, lift can be expected to be proportional to the angle of attack, which is also observed:
This is all explained in more detail in The Secret of Flight.