A common defense in relationships is playing the blame-game.
One version is to pathologize our partner, or conclude that there is something inherently wrong with them. When we pass this judgment, we tend to conclude that they have mental problems. We may even focus on what we know of their childhood and past relationships to support our theory.
The beauty of this defense is that it lets us off the hook: “if they’re flawed, then we must be ok”. This reasoning allows us to draw attention and responsibility from ourselves and place blame on them.