[lmt55]

I would say that the 'mirror stage' is a clear and concrete idea (not necessarily clearly and concretely elucidated by Lacan) which, while it doesn't have the same status as a scientific statement about the mind, provides a helpful illustration, with some explanatory power, of how the 'self' is formed.

(Note that when I say 'a scientific statement about the mind', I would regard very little of the scientific discipline of psychology as meeting this standard. In most cases it is also far less interesting than psychoanalysis.)

Of course, many people are content that they are able to live with a 'sense of self', without worrying about how it is constructed. That doesn't mean that it's not an interesting, useful or accurate idea.