Libido & Desire
Very early in Seminar VI: Desire and Its Interpretation, Lacan points out:
Libido, [which is] a notion that lies at the heart of psychoanalytic theory, is nothing but the psychical energy of desire (p. 4).
He also points out that when a person is defensive, they are often defending themselves from a desire. When a person is being inhibited (consciously or unconsciously), they are inhibiting themselves from attempting to realize a desire.
Another way to think about this might be that when people are being defensive, they are attempting to re-direct the flow of libido (psychical energy) away from a desire towards inhibition.
It seems to me, that Lacan's brilliance is to explain that the symptom is the mechanism that redirects the libido (energy) away from doing what one might want to do, or saying what one might want to say, and putting this libido/energy into inhibiting/preventing one's body from doing/saying what it desires.
When the symptom works people don't come to an analyst. When the symptom does stop working, that's when someone presents themselves at the analyst's door.