That might be true for library-type code, but anything operational is going to have environmental factors that can cause induced misbehavior rather than a pure

That might be true for library-type code, but anything operational is going to have environmental factors that can cause induced misbehavior rather than a pure "bug" from improper implementation. Good debugging tools help induce these things and monitor behavior. For example, I might have a timing problem that I suspect to be related to network, and I can simulate a lossy network.