If you're following this advice, you are either purposefully choosing goals that you do not know how to achieve, which is a problem, or purposefully choosing goals whose achievement relies on way too many externalities over which you have little control, which is a problem.
I'm not saying external factors shouldn't be considered, or that we should only set goals that are within comfortable reach.
Rather, I'm saying the uncertainty should be accounted for differently. It should be baked into our goals, not treated as if it only matters at the OKR level.
Imagine if you were to plan a sprint, and your story points did not factor in uncertainty at all. Then, you committed to a sprint size that also did not take into account uncertainty. But your stakeholders agreed that a 30% sprint failure rate was acceptable.
Now imagine baking in uncertainty into your estimates and then committing to a sprint size you can realistically hit. Add stretch goals if you want. Doesn't that seem more sensible?