You've certainly heard all the dozens of reasons why Romney lost. Many have some validity. Besides the obvious that he had no core and he epitomizes the worst in politicians, I believe they miss a main factor: the Romney effect, or Mormonism.
My logic is this:
Though vote counting will continue for some time and it is possible that enough votes could come in to propel Romney past McCain in total number, I suspect he will end with 59Mish, or about 1 million shy of McCain.
Since Independents voted 51 - 43 for Obama in 2008 (or 52 - 44 by another survey) and 45 - 50 in 2012 (CNN), the net swing is 13 points. 13 points of about 30% is about a 4 point swing. This translate to maybe 3 - 3.5 M votes and partially explains why Obama lost so many votes this year, of the maybe 7M. But as Obama lost 3 - 3.5 M, Romney gained about 3 - 3.5M. If he gains 3 -3.5M Independents, yet loses maybe 1 M in total, conservatives really let him down by 4 - 4.5 million.
How can this be when so many conservatives predicted such an outcome would be the end of the world (and still do) and the enthusiasm to get out their voters was of such intensity? It can't be for lack of spending, considering Obama outspent McCain nearly 2:1, but this year, counting super PACs, was probably slightly outspent by Romney.
Why did 4 - 4.5M not vote and why did the polls indicate a much closer gap than the actual? (Regarding the 11 toss up states according to Real Clear Politics, even Nate Silver had an average 1 point Romney bias, while Real Clear Politics had an average 2.5 point Romney bias.) I suspect that many conservative evangelical types simply said they would vote for Romney, but couldn't bring themselves to pull the trigger for a High Priest from such a very "unique" (euphemism setting on gentle) religion.