Natural, easy, patient, gentle
Campbell gives a two-sided checklist for whether a session is going the right way, and it describes the process rather than the result — which makes it far more useful than any rating.
On one side: natural, easy, patient and gentle. Those, he says, are the hallmarks of a successful process. On the other: result driven, ego driven, success driven, frustrated, forced, fearful, and having preconceived notions and expectations. Those are the hallmarks of a wrong-headed, flawed execution.
Read the second list again. Almost every item on it is a form of trying. Which is why he says, flatly, that you cannot engineer a meditation — you have to let it happen, you cannot make it happen. And that it is not the technique you use, it is the way you approach it.
He does a good impression of the failure mode, and it is recognisably the engineer's: you sit down, you take a deep breath, you relax, you go through all the things, you do this and then that and then you let go of things, and then — nothing happens.
Today the instruction is subtraction. Whatever effort you are applying, apply slightly less of it, and see whether anything is actually lost.