Why must systems engineers test a system against a range of possible inputs?

Systems engineers must test a system against a range of possible inputs because the inputs a system encounters in actual operation are typically stochastic, meaning they function as random variables over time.1

Because these inputs cannot be predicted with absolute certainty, evaluating performance based on a single, precisely defined input is insufficient. Instead, systems engineers must assess performance as a statistical average of the system's responses to a variety of potential inputs to ensure reliability and effectiveness in real-world conditions. This approach is essential for managing the complexity of man-made systems, where extensive interactions between components mean that performance must be robust enough to handle unpredictable operational environments.1