The overarching lesson of my career has been that people are fallible and processes that rely on humans to not make mistakes are bound to fail. Recently I've al

The overarching lesson of my career has been that people are fallible and processes that rely on humans to not make mistakes are bound to fail. Recently I've also been thinking about the importance of being able to reason "locally" about code, it might be the single most important property of a software system. "locally" typically means a function, class, or module, but I think it can also be applied to "horizontal" cases like this. For example, if you add an enum variant the compiler should guide you to reason about each place where the enum is no longer exhaustively matched.