Very true. When transitioning from fan to professional the first thing is to separate the head from the heart. I always used to have a poor record when betting on games that my old team was playing because my heart (one way or the other) would interfere.
Now I know better. There is something in most sports that I call the "Fairytale Factor" and it is something always worth betting on. You see it in the promotion of the games, the commentators start talking about fairytales for a particular player or team. Fans love a good fairytale coming true so it can be a good indicator of what is about to happen. Players believe in fairytales too so they often actually play better when it's on the line.