From a pure engineering standpoint, you're correct. But after starting my own company I have a different opinion: The idea that any work is "Worth doing" more than 10 minutes ahead of time is kinda specious. Everything needs to be evaluated against what's going on RIGHT NOW. People aren't necessarily being unreasonable to interrupt, it's just that the whole picture might not be obvious. Of course there are those who interrupt when they know better, but no process will stop that.