In the philosophical analysis Bunn proposes, ego is defined as more than just selfhood or a knowledge of being an individual, it is more specifically defined as that version of the self which others give existence to and to and by which the individual subsequently allows him or herself to be defined. The example given is that of a well-known contemporary artist who has chosen to define herself very much by the public image she presents of herself and her work.
Of course the point being made here is that, in order to have public success one must have a public 'face' or persona and that, in all practical senses of the term, that public 'face' thus appears to be the real self, or the ego. There is a horrible verisimilitude about this. The artist - and often even in 'ordinary life' the point is valid - thus loses him or herself in that public face and comes to believe it to be his or her real self. Any experience beyond or outside of this facade then tends to become rejected or is assimilated into it. Real selfhood ceases to develop and the almost comic persona takes over. In art this invariably leads to a creative impasse - but of the kind that both the public (including the art establishment) and the artist are unaware. Hidden as both are, behind the established ego.
In the context of the Dix Semblaient Monts, Bunn makes it clear that one must be prepared to adopt this face. It is a price to be paid. But the warning is also implicit: that public face must be not be allowed to take over from the empirically derived and empirically evolving real self. If it is, true individuality and so creativity is lost.