What is a Product Owner?
The product owner owns the what and the why: maximizing product value by managing and ordering the product backlog, writing and clarifying items, accepting or rejecting work, and representing every stakeholder's needs to the team with one voice. One person, not a committee — decisiveness is the design.
The team owns how and how much per sprint; the PO never assigns work or overrides estimates. A PO who can't say no is a backlog that means nothing.
Worked example
Sales wants ten features, support wants five fixes, the CEO wants a demo darling. The PO weighs them against outcome data, puts checkout-abandonment fixes at the top, and tells sales their integration ships two sprints later — to their faces, with the reasoning. The team gets one ordered list instead of three shouting stakeholders. That translation is the whole role.