People in my line of work try to answer certain questions. Why did Hillary surge after misting up in New Hampshire? Why have primary victories produced no momentum for the victors? Why did John McCain win among Republicans who oppose the Iraq war in both New Hampshire and Michigan, but lose among voters who support it?

The truth is that many of the theories we come up with are bogus. They are based on the assumption that voters make cold, rational decisions about who to vote for and can tell us why they decided as they did. This is false.

In reality, we voters  all of us  make emotional, intuitive decisions about who we prefer, and then come up with post-hoc rationalizations to explain the choices that were already made beneath conscious awareness. “People often act without knowing why they do what they do,” Daniel Kahneman, a Nobel Prize winner, noted in an e-mail message to me this week. “The fashion of political writing this year is to suggest that people choose their candidate by their stand on the issues, but this strikes me as highly implausible.”

Nobody really knows how voters think, especially during primary seasons when the policy differences are minute, but it wouldn’t be surprising if the cognitive chain went something like this:

After seeing a candidate for 100 milliseconds, voters make certain sorts of judgments based on expressiveness, facial structure, carriage and attitude. Alexander Todorov of Princeton has found that he can predict 70 percent of political races just by measuring peoples’ snap judgments of candidates’ faces.