Product development is a game with a lot of risk. Product Owners therefore need to have a different mindset than a manager. They are entrepreneurs. People who want take risks based on their best judgment knowing their long term vision.

Prioritization is something you need to do based on a lot of variables. One is business value, one is technical risk, one is market entry. Enterpreneurs know not all of their ideas will be successful.

With Scrum we do have a way to be a enterpreneur with a minimized risk. You try something out for a Sprint, you can bring it very fast to the market and if it fails, than you put it out of the market place again.