PROTEUS Than men their minds! 'tis true. O heaven! were man But constant, he were perfect. (5.4.7)
After Julia reveals her true identity as a woman and declares that it's worse for men to change "their minds" than for women to "change their shapes" (cross-dress), Proteus suddenly realizes that Julia is right about his behavior – he's been falling in and out of love and his inconstancy makes him flawed. Literary scholar Marjorie Garber points out that, at this moment in the play, Proteus's true nature is "unmasked" at the exact same time that Julia's true identity has been revealed (Shakespeare After All, 46).