There is no blame in this
Campbell's instruction for what to do with an intruding thought never varies, and the verb is always the same. Gently put them aside, and refill your mind with the mantra. Not fight. Not banish. Not analyse where it came from. Put aside, gently, and refill.
The gentleness is doing real work. He pairs it with the observation that if you ever become frustrated, you are trying too hard — frustration is not a sign you need more discipline, it is the diagnostic that tells you your approach has gone wrong.
And then, unusually for this genre, he removes the moral dimension entirely. There is no blame, he writes, no reason to feel badly, and no failure on your part. Continue to apply the process gently and consistently and one day, when you relax, success will take you by surprise.
Notice what that sentence does. Success arrives when you relax — not when you concentrate harder. It takes you by surprise, meaning you were not watching for it.
Today, count nothing. Every single time you notice you have gone somewhere, that noticing is the practice working, not failing.