Process principals are like design patterns in software. They aren’t created as much as they’re discovered. It’s my belief that agile was created the same way. Someone had a team that was working really well together and someone on that team decided to try and figure out why, so they came up with a set of principals and decided to call it agile methodology.
Many teams follow these principles blindly, which is utter madness. Process can never be a substituted for good judgment. The intent of these principals is to attempt to guide the team to some best practices, not tell them how to work. Every team is different and thus every team is going to vary in those principals. It’s important to not dictate how a team should work, but rather guide them in some common sense methods.
Being productive is about finding the best way for a team to perform, not restricting yourself to a particular set of rules someone who has no knowledge of you team said you should do.