Once people are in the position to gain from not being happy they will never be happy, "appetite comes with eating".
Sorry if this is a common expression.
I believe the idea expressed in ‘appetite comes with eating’ is that your desire to indulge in an activity is correlated (caused even) with that activity. IE skydivers will likely have a larger appetite or desire for skydiving than a layman.
In a larger context I believe cjbgkagh is arguing that women can retain an advantageous position in a marriage by pretending or presenting unhappiness because exiting a marital contract would be an especially poor outcome her partner.