Falling for your own illusion, when you allow your "angle" of which you use to attract a girl to consume you and you actually become said illusion, which usually results in you entering a relationship with that girl. The only way you can break this is to find the things she dislikes (keeping in with the persona) and work it into the illusion, otherwise you break the illusion and all ends terribly.
Think with the upstairs and not the downstairs. Your motives can still come from the downstairs, but make sure the ideas and executions are from up stairs. If you need clarification upstairs is the head on your shoulders, and downstairs is the head below your waist. When you think from downstairs you can easily get caught in a relationship you don't want to be in, and you'll only be in it because of your downstairs thinking. Ways to tell if you are letting the downstairs take control, you don't really like the chick but when around her you find you are going into "boyfriend mode". This means cuddling and holding hands during a movie, ect. Now it only applies if you do not like the girl, if you do actually like her your in the clear to go full boyfriend mode. The best way to tell if you are doing it is when you with her. Even though your in boyfriend mode, you still think against what your doing, or are thinking or other girls/picturing her as another girl. Another method of telling is after she has gone, if you feel excited, giddy, happy, and can't stop thinking about her, your in the clear, if you have major doubts, are thinking why did I do that, or thinking major time about another girl, you have to get out of it as quick as possible, because downstairs is doing all your actions for you. Just a quick note, if you continue going through with it, the relationship won't last very long, it could easily end badly, and its not a one night stand so don't treat it as such!