Somewhere in your first few hours of ground school, someone probably told you this: air splits at the front of the wing, the top surface is curved so the upper air has farther to travel, it has to speed up to rejoin its partner at the back, and faster air means lower pressure — so the wing gets sucked upward.
It's a tidy story. It's also wrong, and not in a small way. There is no law of physics that says the two parcels of air must rejoin at the trailing edge. When you actually film smoke pulses crossing a wing, the air over the top doesn't arrive at the same time as the air underneath — it arrives earlier. The upper flow outruns the reunion the story depends on. NASA keeps a page dedicated to debunking this "equal transit time" theory, and Holger Babinsky's wind-tunnel footage at Cambridge shows the mistimed arrival directly.
So throw the story away. Here is what's actually happening — told two ways, because there are two honest ways to read the same event.
The momentum ledger
Hold a wing at a slight angle to oncoming air and it does one big, unsubtle thing: it turns the air. Flow that arrived level leaves the trailing edge angled downward — pilots call that downward river the downwash. Air has mass. Deflecting tons of it downward, continuously, requires a continuous downward force from the wing.
Newton's third law does the rest. The wing pushes air down; the air pushes the wing up. That reaction is lift. No curvature mysticism required — which is why a flat balsa wing, a paper airplane, and an aerobatic plane flying upside down all manage to fly. What matters is meeting the air at an angle that turns it downward.
The pressure ledger
The other honest reading follows the pressure. Air doesn't touch the wing with anything except pressure (and a little friction), so whatever lift exists must show up as a pressure difference between the top and bottom surfaces.
It does — but not because of path lengths. Watch the streamlines: over the top of the wing, the flow follows a curved path. Making air follow a curve takes a net force pulling it toward the inside of that curve, exactly like a ball on a string. For air arcing down over the wing's upper surface, that force can only come from pressure being lower near the surface than in the air far above. So the pressure on top drops. Under the wing, the flow is deflected the other way, and pressure rises a little. Low pressure above, higher pressure below: the wing is pushed up.
Notice what this version does not claim. It doesn't say the underside does all the work by catching air like a skipping stone — another retired theory NASA keeps on file — and in fact the pressure drop above the wing typically contributes more lift than the pressure rise below. And it doesn't abuse Bernoulli. Bernoulli's principle — faster flow, lower pressure along a streamline — is real physics; it is Newton's second law applied along a streamline, nothing more exotic. The equal-transit story wasn't wrong because it used Bernoulli. It was wrong because it fed Bernoulli a made-up velocity.
One event, two ledgers
Here's the part that ends a thousand hangar arguments: the Newton telling and the Bernoulli telling are not competing theories. They are two ledgers for the same transaction. The pressure differences and the turned flow happen together, cause each other, and each accounts for exactly all of the lift — you sum one or the other, never both. Argue "Bernoulli versus Newton" and you've already lost; the correct answer is yes.
Why a pilot should care
Because the honest version puts the right lever in your hand. Lift isn't a property of the wing's shape that you bought with the airplane — it's a deal renegotiated every second between the wing and the air, and the term you control is the angle at which they meet: the angle of attack. Turn the air harder and you get more lift — up to a limit, and the limit is sharp. That limit has a number, and it's the subject of The Stall Has a Number.