The Mirror Stage is a theory about human development first posited by renowned French psychoanalyst Jacques Lacan. He believes that the first time a child recognizes itself in a mirror (not just as an image, but as that of its own actual self) is when the fundamental concept of personal identity begins to foment from within.
That one moment is the very beginning of our internal sense of self, as well as the creation of the subjectivity with which we view the world from that point forth.
The selfie, an invention of the early 2010s, can only be construed, in this context, as an intentional infantilization of our experiences. The desire to return to a simpler time, when our selves were the only thing that mattered.
Selfies are personal attempts at regaining the control that is lost as we age, as we become more aware of the world around us.
And in this one, Nina Agdal is wearing a nice, white bra.