Originally aircraft were most designed around several principals. The main principle was probably to make the aircraft as stable as possible so that the plane would not suddenly change directions or altitudes without the pilot telling it to and also so that it made the plane easier to control. After this would come characteristics the plane would have such as designing it to withstand high speeds or be able to lift large amounts of ordinance.
As time has passed airplanes have become less dependent on the stability principle with the development of technologies to make the plane more stable without changing the basic airframe design. The most recent of these technologies is a small built in computer that actually compensates for an aircraft's instability and therefor causes the aircraft to fly straight.
Therefor present day aircraft no longer have to consider stability as the main principal instead very recent aircraft were designed with keeping a low radar signature as their main principle. Stability still has to be considered but not as much. Other lesser principles are range and designing the airframe to withstand high speeds.