Here’s what happened. The Dem primary was a real fight and a lot of hearts were lost when Martha Coakley won only by turning out her base. MA Democrats already dislike defeat of their candidate which is why Republican Governors were elected here for 16 years. After the primary, Coakley’s team incorrectly decided that the game was over and they won.
Meanwhile, the media decided to find out who this other character “challenging” her was. Scott Brown began to get press and the Coakley camp was still silent. In fact, Coakley’s campaign never really reached out much further then the initial base until after the New Year when the polls began to close in.
Independents and Dems tired of the arrogance and hubris that the party has become known for here in MA, began angrily answering polls. The momentum strengthened and the RNC injected money into MA for the first time since who knows when. Brown took the underdog roll, one which MA loves and stuck through it with a smile.
Shorter version: don't get comfortable. Hustle. Hustle. Hustle.
Or just listen to M.I.A.