The opening trope of the second chapter of the Zhuangzi is a source for numerous insights into the Zhuangzian perspective, but I, at least, have never been able to understand its meaning as a whole. It begins with a disciple finding his master in a trance ("body like dead wood, mind like dead ashes") and when he inquires as to what's up his master answers, "I have lost myself." His master then proceeds to explain what this means through his description of how "the Great Clump" belches forth the wind (qi) which, passing through the forest, enables each tree to give forth its own unique voice. The problem is how this answers the questions of what it means to lose oneself and how that can happen.
Before considering a possible answer to these questions, a quick look at how "I have lost myself" might be worthwhile when compared to the optional translation, "I have lost my self". The difference, of course, is that the latter assumes a discreet "self" to lose whereas the former would seem to indicate a more general loss of self-preoccupation. The truth is, there is no self to lose.
Meanwhile, back in the forest, "the myriad sounds produced by the blowing of the wind are different, yet all it does is elicit the natural propensities of the hollows themselves. What need is there for something else to stimulate them?" (Mair) This statement concludes the metaphor and would seem to declare its central point to be that things just happen of themselves; at most, the wind simply provides the opportunity for each thing's spontaneous self-expression (ziran). Other translators have, "What need then is there for a Rouser?" None. From the Daoist perspective, there is no Prime Mover or First Cause; each thing arises of itself, or as Guo Xiang has it, "spontaneously self-generates" (though he is careful to clarify that this does not mean a self that creates, but that it is "Heaven-so", "what is not deliberately created [by self or an other].") (Ziporyn)
Should we doubt this to be the main point of the metaphor, Zhuangzi's further elucidation seems to make it clear. In what follows he tells us that all human experiences are "like musical sounds from empty tubes . . . The instant one grasps this, one understands from whence they arise!" They arise from emptiness, from nothing. But this is not Nothing predicated as something (Non-Being), but the nothing that simply signifies the utterly unknowable, and therefore inapplicable.
How does this explain the master's loss of himself? As is generally the case in Daoist thought, one emulates the macrocosm; the master lost himself because he gave up the idea of having a self that is in control. There is no "rouser" within, a 'self' which controls one's unfolding into the world. Rather, it all just spontaneously arises. To lose oneself is to let oneself happen without deliberately trying to make it happen. It is to let the "Heaven-so" be "Heaven-so". True control, Daoist control, is the ability to cede control.
You can check out Scott's writings on Zhuangzi here.