Let's go one step higher, keeping track of the state by a state machine. When designing/coding with the correctness on mind, I try to stay focused, and not think of edge cases. Or I will end up spending more time coming up with edge cases and what can go wrong. I'm not lazy, I'm almost certain of that. But I do feel time is a limited resource and want to add more value per hour spent working. Maybe, this is more the case of if it can be automated then automate it.