The old rebbe explains in the 27th chapter, that if the sadness which falls into him is because bad thoughts come into his mind, if they come during his busyness, he should be happy through thinking that through this that he pushes away the bad thought he is doing a mitzvah, and without this bad thought he would not have this mitzvah. And even a benoni has bad thoughts, but right when they come to his mind he pushes them away.