Either that, or he delegated too much authority to out-of-touch campaign managers who fed him bogus internal polls.
Perhaps he believed in some sort of LDS Church "predestination" prophecy that he'd win, and overlooked the details of effective campaigning.
Most likely, he just overestimated the intelligence of some segments of the electorate. He and Ryan were too wonky, and could not bring themselves to dumb down the campaign to get enough ignorant voters in swing states.
C'mon man they didn't use any wonky ideas for smart people they spent time catering to the Trumps who thought Hawaii was part of Kenya.