It would be convenient to assume that the sound systems we use always work but it would be unwise to do so. Just because a sound system seemed to function properly the last time we used it gives no evidence to suggest that it will function properly the next time. Why? There are multiple reasons that a sound system fails. One of them is simply the passing of time. Another is neglect. Another is abuse. Who last used the system? Yet another is sabotage. Not sabotage as if someone wanted to break it but sabotage as in someone thought they can improve it and so they undo whatever the original team put in place. Consequently, unless you have the tools and skills it takes to verify a sound system, you’re relying on hope and faith for your next production.