The principle that the observation is the judge imposes a severe limitation to the kind of questions that can be answered. They are limited to questions that you can put this way: "if I do this, what will happen?" There are ways to try and see. Questions like, "should I do this?" and "what is the value of this?" are not of the same kind.
The Meaning of It AH: Thoughts of a Citizen Scientist, Chapter I (p. 16), Perseus Books. 1998