Identification. Highly involved fans identify with properties (teams, players, entertainers) because fans find them attractive in some meaningful way. We identify ourselves with others (universities, teams, individuals, and even brands) because we believe it says something positive about us to others. We gain social acceptance. We identify with winners and we avoid losers, unless we can think of some other reason being a loser isn't so bad. For the highly identified fan, what happens to the team feels like it's happening to the fan--so some part of the experience needs to feel good for the fan to continue being a fan.
Passion & consumption. When a fan identifies with a property, the property becomes the object of a passion that consumes the fan's heart, soul, mind, and, ultimately, time. And time means money. Passionate fans spend time consuming media (TV, radio, print, websites, social networks, mobile data), meeting with other passionate fans at the game, bar, tailgate, or house, and buying merchandise to demonstrate to others how passionate they are. How else do you explain the Twilight phenomenon?