Current fighter jets are aerodynamically unstable. However they are also computer controlled. The flight computer makes tiny adjustments continuously. For basic maneuvers they are easy to fly. The difficulty comes from the immense power. A fighter pilot can also use an autopilot for cruising long distances or for special attack maneuvers like toss bombing.

The reason fighter pilot training is difficult are the physical requirements to be able to sustain high G maneuvers, spatial orientation, ability to act calmly in high stress situations, planning missions including fuel calculations for different loadouts, and operating a very complex machine with dozens of systems and weapons.