The product owner responsibility is to maximize product ROI, however, priority is a hard decision
Facing the hard facts as soon as possible, no matter what it takes
Do you know who is your customer?
Do you know what is main problem you are going to solve for him?
What is going to be considered success in the next release?
What is the most valuble thing for your customer in your solution?
Where is the risk?
If you will know how to answer those questions, you probably can create safe release planning - all you need is smart priotization