OKRs are assumptions
Every decision you make on what goals to pursue is based on the best information you have at the moment. It’s a guess. Or if that word sounds too unprofessional, it’s an assumption.
You’re assuming certain customer behavior changes will happen if you build and design the right set of features. As much as your solution hypotheses can be wrong, sometimes it’s the goals that we’re targeting that are wrong because they, too, are assumptions.