Those are micro level features. For mission critical module like this, it is unlike those low-level bugs will be left without notice. But the true complexity i

Those are micro level features. For mission critical module like this, it is unlike those low-level bugs will be left without notice. But the true complexity is coming from states, and combination of states, and many of those are unknown to the developer until certain incidents kicked in. Good programming practice can't relieve programmers from the cognitive burden of reasoning the outcome of those combinations.