Freud, and the Analysts who proceed in his path, see all things sexual, (and sometimes all things), through the lens of the penis. A penis which they feel inspires just one emotion-envy.
I can only assume that the lens is rose tinted, for why else would a penis be envied in this way?
Of course, we are all indebted to Dr Freud, not least for him bringing the unconscious into our awareness. Penis envy can be understood at this level too, as an underlying envy or anger experienced by women who feel, or are made to feel less good about themselves in relation to men. However, a more literal interpretation seems equally valid when considered alongside other aspects of Freud’s sexual perspectiv