Although Knife in the Water actually emerges in retrospect as Polanski's least completely personal work …, it nevertheless does contain all that is thematically essential to him.

The expensive yacht, the beautiful young wife who shares it with him, and the private sea upon which it rides started out as status symbols which Andrzej felt compelled to attain. The film begins at that point where he has attained them and where their illusory protectiveness has created for him a private world, a world which is intruded upon by the student, and destroyed. This theme of isolation wherein the protagonist or antagonist's private world is intruded upon by strangers, a situation which always ends in some form of violence, self-destruction, or disaster is, in fact, the nucleus of all of Polanski's films….

[In Polanski's films] couples are always significantly mismatched due to the neurotic obsession of one partner (or both...