It's an extremely scary thought, isn't it? I have a lot of experience with criminal psychology (mostly through my work at the police department and my psych/English classes), and obviously I was assaulted. Keep in mind, though, that I'm not a psychologist - I'm no expert; I just have had an interest in psychology for years.
This may trigger, so be in a safe spot, k?
I hate to say it, but yeah, many rapes are premeditated from what I can tell. Mine was premeditated...he had the intention of having sex with someone, of getting a girl to "go out" with him and probably of forcing her to do whatever he planned, even if she didn't want to. And he picked me, but what really infuriated him was that I turned down his advances. So when he heard that I'd left the party, he got a knife and slipped around the outside of the house and waited until I'd turned my back to where he was hiding. Then he jumped me. He had it planned out - he subdued me with the knife and brought me to his car. I later found out that he was planning to take me back to his apartment or something after he'd raped me once.
Obviously, we all know that it's a power thing. Many rapists - again, this is just from my research, I'm not an expert - fantasize about raping someone before and after they do it. It's disgusting. Often, after the fantasies no longer "work" for them, they'll go after someone else. Many rapists are serial rapists.
Take care, everyone.