“The only person standing in your way is you.”

Nina’s bulimia and inability to adapt to the role of Swan Queen shows her compulsive personality. It is likely that she developed these characteristics because of her overbearing mother, who maintains tight control over her. This creates an inner struggle, which the director makes apparent through the use of mirrors in Black Swan. On numerous occasions when Nina is gazing at her reflection she notices her reflection doing things outside of her control. This depicts the conflicting personalities that reside in Nina, potentially suggesting that she struggles with schizophrenia. 

Nina fights to control the alter ego that attempts to take control of her. In the scene before her performance, she attacks the mirror in her dressing room when she sees the Black Swan as her reflection. While Nina’s personality before being assigned the role of Swan Queen is obsessive, this role requires her to transform into a loose and passionate ballerina. When she looks into a mirror and sees the sexual and dangerous black swan looking back at her, she is frightened. Yet the reflection in the mirror is what she must strive to become.

When Nina shatters the mirror in her dressing room, she becomes one with her alter ego. Thus she breaks the barrier that is preventing her from truly becoming one with the Black Swan.