This works to quite brilliant effect during a particular climactic moment when, on the foot of some really monstrously callous behavior toward Charlie at a juncture at which she had clearly hoped for a reconciliation, Sarah delivers a long, spiteful speech that gently but comprehensively upends our sympathies and invites a whole new reading of their relationship. In it, Sarah outlines all the ways she feels that Charlie, who casts herself eternally as the victim, has herself been the cruel one; her passive-aggression and instinct for martyrdom are tools for manipulation just as powerful as Sarah’s more openly hostile, and, despite all her lies, somehow more honest behavior. If a friend should be a true mirror, at exactly the point at which they become irrevocable enemies, Sarah is perhaps the truest friend Charlie could have--it’s just a shame that the one major sour note the film strikes is in the overdramatization of Charlie’s reaction to those very revelations.