It's really a fine line, I think. You cannot do everything and you cannot discuss everything. Unfortunately, you also often cannot undo such a decision cheaply

It's really a fine line, I think. You cannot do everything and you cannot discuss everything. Unfortunately, you also often cannot undo such a decision cheaply later. (One of the big fallacies of agile software development is that making changes has essentially constant cost of effort, whereas in reality changes get more costly over time.) So the only way out is some kind of agency/ownership. Every team should have a basic understanding of the goals of the stakeholders so they can make such decisions in good faith.