Well said. Code stays as it is, typically. Data changes. Of course code can modify its own 'code". But that makes it much more difficult to reason about its be

Well said. Code stays as it is, typically. Data changes. Of course code can modify its own 'code". But that makes it much more difficult to reason about its behavior. It is good to have some "invariants". If we can assume that code does not change except when the human author changes it, then it becomes much easier to reason about the changes the program may cause to the data.