Everyone has his or her own interpretation of why Brown won and Coakley lost. Which is why the aftermath of this election is likely to be as acrimonious as the election itself: No one can prove or disprove anything. Even more than usual, the pundits and analysts don't really know what they're talking about.
There's only so much we can learn from this election, largely because there were no exit polls. Normally, a consortium of news organizations pays a company to conduct surveys outside polling locations—but only when there's enough interest in the race to justify it. By the time national media started paying attention to the race, it was too late.
As a result, we don't know to what extent independents swung to Brown. We don't know how many women voted for Brown instead of Coakley. We don't know whether Obama's appearance drew more African-Americans to the polls than usual. We don't know why voters favored Brown, or when they made up their minds. Perhaps they liked his ideas on health care, his plan to keep Guantanamo open, or his smile. For all we know, his truck sealed the deal.
Read the entire thing, it's worth a look.