It refreshes him, to have regular periods of emptying out, of being nothing. Identifying as “I am this”, “I am that” requires a lot of energy, making him tired. To become nothing, he has to take out the trash accumulated in his mental/emotional house.
When taking himself too seriously, or not seriously enough, me might say: “I am nothing!”, or, failing that, “I am everything!”
Then body can relax. He sits, spine erect, breathing into his whole body, as into a tube of light, every night before sleep. Maybe only a minute. Maybe half an hour. He takes out the trash, contemplates that which requires further action, then puts “the processor” to sleep.
He had previously encountered a similar idea in Byron Katie’s “the Work”, in which she encourages the question “Do you know? Do you really know? For sure?”
More often than not, especially around triggers regarding other people, his answer is “I don’t know”.
When he wants to complain, or feels angst, he says: “I don’t know”. The result, often, is peace of mind. He loses ability to worry. If worry persists, he finds it’s an indicator of deeper emotional dynamics needing attention.
Why does this work? I don’t know!