A person might have an ideal self where it harbours all good qualities that it wants to acquire. A person might also have an evil self where it harbours evil qualities that it wants to distance itself from. This is just a development of Carl Rogers view of self.
Tranference might simply be the projection of the patients ideal or evil self onto the therapiest. If the patient has a positive view of the therapiest he probably projects the ideal self and the evil self if the opposite is true. Falling in love with the therapiest therefore has to be viewed as somewhat narcissistic. Love is to my understanding the identification of thoughts or behaviours in an other person that oneself has.
The media that makes this projection possible is that we see the therapiest as an authority and makes the connection power and good. Seen in this view projection of evil might be from viewing the therapiest as powerful and projection of good because we see the therapiest as good and/or powerful.
Tranference is as such proof of a somewhat disintegrated self or to use the words of dr. Phil "You are not fully your authentic self".