The ego is a construct.
For Lacan, the ego is a construct, meaning that it is an imaginary answer to a real problem, and when the mind invents the sense of self, it is largely speculative. Therefore, adult psychology is rooted in beliefs that were formed about the world when the person was only an infant. This begins a continuous process of self-perception and constitutes a kind of dualism—real physical reality, and the world in tension with the imagined self.
Children aren't born understanding objective reality.
When children are born, there are many interesting phenomena surrounding their perception. The one that means most to Lacan is the puzzle of understanding one's own reflection in a mirror. Lacan argues that the ego is essentially a response to the fact that we have mirrors now, and we get to see images and symbols of ourselves in a much more overt way than we were naturally programmed. So the ego is a child's best answer to understand their own physical appearance. This means that the children were not born with ego, and their relationship to objectivity and the physical world is still a problem an infant is solving.
Lacan believes Freud's approach would be helped by a linguistic understanding of how the mind works.
For Lacan, Freud's ideas were a demonstration of a linguistic organization of the mind, especially around lapses in thought, Freudian slips, interpretations of dreams, and so on. Freud would like disagree, but Lacan shares this point of view with Noam Chomsky who also wrote extensively about the way language forms perception. Concepts are represented by words in the mind, associated to images. So dreams might also be connected to language in that way.
Early childhood is largely a mystery, but it governs our adult behavior.
This is the theme that makes Lacan similar to Freud—the belief that early childhood holds the secrets to understanding the perplexing state of human self-perception and psychology. Their similarities continue into the interpretation of dreams, the phallic and Oedipal problems, but their understanding of the subconscious is different.
Basically, Lacan believes that early events of brain development govern our perception of the world throughout our lives, as the infant comes to understand itself as an object in a physical realm.
