Mirror Stage
Let's begin with the first Lacanian concept I ever came across; the mirror stage. To put it simply, it is when an infant is able to see and register their reflection in a mirror, and thus learn of their position relative to their mother (i.e. my mother is a woman, and I either look like her or I don't). It typically occurs as early as anywhere between 6 to 18 months of age. Keep in mind everything revolves around the mother or the lack thereof.
This might remind some of you of what Sigmund Freud said about the Oedipus complex. Sure, both ideas are interlinked, but it is crucial to understand the difference between them. While Freud's Oedipus complex focuses on the child’s unconscious desire for the opposite-sex parent and rivalry with the same-sex parent, Lacan's mirror stage is more about the formation of the ideal "I"—the ego. It's about the infant's recognition of themselves as a separate entity, marked by the image in the mirror, which is then influenced by their relationship to the mother. In Lacanian terms, this recognition is not just about seeing the reflection but about the desire for wholeness and cohesion, something the infant perceives but cannot fully achieve. This process lays the groundwork for how we relate to ourselves and others throughout life, with our sense of identity continually shaped by that initial moment of separation and recognition.
I'm going to elaborate a little further. While the baby identifies itself, it also feels confused, as though it is having a recurring out-of-body experience. Almost like "the image is me and simultaneously not me" or, "'I'm looking at myself right now, but I am also embodying somebody else, seeing me from an outside perspective."