When there is clear owner for each Key Result, Milestone or action, that is when OKRs are successful.

Orphan Key Results or actions with no owners are often a sign of danger. On the other hand, sometimes KRs (Key Results) or actions have more than one owner which can also lead to lapses in achievements of Goals and Key Results. 'Being accountable' fundamentally implies responsibility towards Outcome or Key Result. While ownership is the initiative, accountability is the follow-through.