It's also important that the Product Owner maintains a clear view of the current business problem our team is being asked to solve, typically in the form of a simple mission statement.
For example, the following is a real team mission statement:
Enabling new methods of content display, navigation, and discovery.
The mission statement should give our team enough guidance so that we can quickly know if we are on course or if we've deviated. At the same time, it should be broad enough that we can maintain some freedom regarding how we provide solutions. It definitely should not describe how to do something. Instead, it should describe what we are doing.