Romney and his campaign had gone into the evening confident they had a good path to victory, for emotional and intellectual reasons. The huge and enthusiastic crowds in swing state after swing state in recent weeks - not only for Romney but also for Paul Ryan - bolstered what they believed intellectually: that Obama would not get the kind of turnout he had in 2008.
They thought intensity and enthusiasm were on their side this time - poll after poll showed Republicans were more motivated to vote than Democrats - and that would translate into votes for Romney.
As a result, they believed the public/media polls were skewed - they thought those polls oversampled Democrats and didn't reflect Republican enthusiasm. They based their own internal polls on turnout levels more favorable to Romney. That was a grave miscalculation, as they would see on election night.
Those assumptions drove their campaign strategy: their internal polling showed them leading in key states, so they decided to make a play for a broad victory: go to places like Pennsylvania while also playing it safe in the last two weeks.
They actually thought they were going to win Pennsylvania, Wisconsin, Minnesota, and Iowa, maybe even Michigan. They thought Florida, Colorado and Ohio were in the bag as a result. They bought into the bubble and it cost them everything.
Secondly, their ground game was horrible, as BooMan points out.
After reading a variety of articles with sources from inside the Romney campaign team, I am considering revising my whole way of looking at this election. I knew, because I witnessed it first hand, that Romney had a terrible ground game that basically threw money at problems rather than organizing in any rational way. But I still can't believe that they just wasted 30,000 volunteers on election day by asking them to sit inside precincts and strike voters off the list as they voted using a web application that didn't work. Failure on that level is reminiscent of the post-invasion plan for Iraq. It's not a matter of the Obama campaign staff being better. The Romney campaign sabotaged their most passionate warriors and rendered them useless.
If there's one word that sums up the Romney disaster, it is "entitled". They thought they were entitled to win, they were entitled to the Presidency, they were entitled to the vote, they were entitled to fawning media coverage, they were entitled to coattails that would make then GOP heroes, entitled to victory, because they were who they thought they were.
Mitt Romney never had to work for anything in his life. It was given to him. That sense of entitlement sabotaged his campaign from the very beginning. The notion that anyone would every question his victory simply never occurred to the man, because he was never questioned before. He just came out on top because that's the way the world worked for people like Mitt Romney. They won because they were the winners. Only losers ever considered losing, and those rules of gravity just didn't apply to Mitt. He was the destined one. Dubya, for all his faults, at least had been tempered by his humility and his battle with alcoholism. Not Mitt.
And that attitude swept down the campaign. Only losers prepare to lose. Only losers make "corrections" and "adjustments". Mitt had already won the election, it was all just a giant set of bureaucratic trivialities that had to be weathered before the White House was theirs. This was Mitt's test. Ann Romney, especially, displayed this attitude of "why don't you people treat him as the President he is?" They had been running victory laps since May. The first debate convinced them they had won completely and utterly. You could see it. They had "visualized victory."
Only, something funny happened on the way to the Oval Office. Reality stepped in and slapped the bejeezus out of these entitled pricks as the country revolted against these assholes. Barely. But it happened.
And it's a damn good thing. Could you imagine these clueless, entitled bastards running the country? They would have made Dubya look like a Boy Scout.