System stability can be a major problem in badly designed closed-loop systems.

• A. Stability
• B. Usability
• C. Security
• D. Scalability

Answer: (A)

Stability is what matters when a system uses feedback to control itself. In a closed-loop setup, the controller continuously uses sensor information to adjust the actuator. If the design is off, the feedback can amplify disturbances instead of damping them, causing responses that oscillate or grow without bound. A stable closed-loop system, by contrast, returns to a steady state after a disturbance and keeps its output within reasonable bounds.

Understanding this helps you see why stability is the best choice. If the loop is well designed, changes in the input or slight delays won’t cause runaway behavior; the system settles. The other aspects—usability, security, scalability—are important for different reasons, but they don’t describe whether the feedback-driven dynamics will stay controlled or become unstable. For example, a thermostat that overshoots and oscillates around the setpoint illustrates how poor feedback can destabilize a system.