Any kind of vehicle, be it land, air, or water, will keep the nose in front as long as the center of pressure is aft of the center of gravity. Yes, even land vehicles. So what if the pressure is provided by tires on the road? As long as all of the pressures exerted upon the vehicle wind up aft of the center of gravity, the front will stay in front. Some rear-engine sports cars are known for how easily they swap ends if not handled carefully, while the family sedan needs quite a bit of work to have the same thing happen. On ice, the tires provide no force, so the car can spin around easily.

On an aircraft, the projected side and vertical areas are designed so that, again, the pressures put upon the airframe by the air moving past it result with the center of pressure aft of the center of gravity. Now, when the aircraft moves through the air, the forces push it to an attitude where the center of pressure is behind, so the nose is in front.

If the side area was the same forward and aft of the center of gravity, putting the center of pressure on the CG, then the aircraft would have no tendency to hold any position at all.

A weather vane is a good example of this in action. The pivot point is the center of gravity. You have a long rod with fins at one end and a weight at the other. The side view shows a LOT more side area on one side of the pivot than the other, yet the vane forward and aft of the pivot point weigh the same. When the wind blows by, the side with more area is moved with the wind until it's directly behind the pivot. If you made a double-ended weather vane with both ends having the same-size fins, then it would just as likely present itself flat-on to the wind as it would in trail with the wind, or at any other angle.

If the airplane has a tendency to keep the nose in front, then it's positively stable on that axis. This goes for both pitch and yaw. In a tailslide, then, this will make the aircraft flip end-for-end.

That's the 'raw' stuff. When you start adding things like trimming for airspeed and such, things get a lot more complicated