Personally, I believe psychopaths deliberately target a certain type of individual. They really do need to be associated with a predator species because ultimately they follow the same instincts.
IME, their victims are often very compassionate, more forgiving than many, and sometimes, in some way, vulnerable. This vulnerability could be something as mundane as losing your job - a psychopath will look for cracks and seek to exploit them. They study their prey. All it takes is a moment of exposing too much of yourself and you're hooked before you even know what happened. I was reading a study just yesterday about incarcerated psychopaths...psychology grad students were asked to interview them and each grad student walked away from their interviews absolutely convinced that the convict had been wrongfully convicted and was innocent - until they read the convict's previous psych history. Almost anyone can be manipulated by a psychopath.
Even when you know all the 'symptoms' experiencing a psychopath in print and having one target you are worlds apart. Nothing can prepare you for the headiness of having someone so incredibly into you - so desperate to make you happy. They tug at your heartstrings, regaling you with believable accounts of how they've been mistreated by so many. They use your greatest hopes and deepest fears against you. They take advantage of your trust, sympathy, kindness, etc. If they feel you're losing interest, they'll guilt and shame you into staying in the relationship. They'll show you moments of what appears to be pure adoration to suck you back in. And over time, it kinda becomes a game of tug of war with the psychopath escalating psychological abuse (at least) to keep the victim in their grip. Just like any other abusive personality, a relationship with a psychopath is always, ultimately, about control.
JMO and FWIW