Stability is concerned with what happens to a system that is in equilibrium if it is acted upon by a minor disturbance.
If it is stable it returns to its orignal state following removal of the disturbance.
Unstable systems change to a new state following minor disturbance.
Architectural structures must be stable systems.
To achieve stability most architectural structures require to have elements inserted that are not part of the primary load-bearing system.
These are called bracing elements.
Provision of a bracing system is an essential consideration in structural design.