Structuralism was in the air, too, and Lacan offered a structuralist Freud. That is it in a nutshell, and that is what needs explaining. In other words, desires emerge through words and images. They speak a language parallel to our own. Jean-Paul Sartre's followers had no interest in such things.
Existentialists believe in conscious decisions.
The unconscious seems far too squishy to them, too much a denial of responsibility. Instead of internal conflicts, Sartre said, other people create our identity. Lacan picked up on the unconscious as a social being. He even spoke of a child's passage through a mirror stage , in which it must learn to see itself from outside before it can have an internal identity. Yet the psychologist refused to dismiss the reality of an unconscious mind.