The yogis act “for the purification of the self” (ātma-śuddhaye) — and one may object that this too is a desire, and so still a bondage. The reply is that there are desires which feed the ego and desires which dissolve it, and only the first bind. The wish for a bigger house thickens the wall of “I”; the wish for purity thins it, and is designed to consume itself at the end, like a stick used to stir a fire that is then thrown into the same fire. This is sometimes called śubha-vāsanā — the wholesome tendency that undoes the unwholesome ones and then quietly departs. Until the goal is reached it is not only permitted but necessary; only a fool would refuse the raft because he must eventually leave it.