Were the polls wrong? To some extent they were. What was worse though was our understanding of the polls. We took them at face value. Whether it was the media, the pollsters or the public in general, we talked about the polls in a deterministic way. Nate Silver's website, on the other hand, presented its results in a probabilistic manner. If we look at those results, things start to make a lot more sense. Yes, the underlying polls were inaccurate, but Silver adjusts for this to some extent.
As we have discussed before, the quality and accuracy of projections coming out of Monte Carlo depend squarely on the model being used as input for the projections. Silver tries to make the model a better one by adjusting the poll results. I am not sure what the Nate Silver secret sauce is, but my guess would be it involves looking at past performance of the particular poll. Also, Silver looks at a multitude of polls and combines their results. This results in a model that is not influenced greatly by one incorrect poll. It is most likely, a weighted combination where historically better performing polls have more of an impact than the more inaccurate polls. A great description of how the adjustments are done to the polls is available on Nate Silver's website - http://fivethirtyeight.com/features/a-users-guide-to-fivethirtyeights-2016-general-election-forecast .
Silver then runs the simulations based on these adjusted polls. After running 20,000 simulations using a thoroughly well-adjusted model, Silver's team is now able to project probabilistically, what are the chances of each candidate winning the election. This was what the forecast looked like on the eve of election day.
What the above result means is that more than 1 out of 4 simulations resulted in Trump winning. Hillary had about a 70% chance of winning the election. Yes, that is a greater probability than what trump had, but it is around the same probability as that of rolling a 3 or more on an unloaded, 6 sided die. It is by no means a slam dunk.
...the probability of an attempted dunk being successful in the NBA is about 93%. That is more than 20% greater than the chances Hillary Clinton had of winning the election.
This is where our understanding of the polls was wrong. Yes, the polls themselves were not very accurate, but our understanding of them was even more flawed. Let us think about it in terms of a slam dunk. According to http://www.basketball-reference.com/ the probability of an attempted dunk being successful in the NBA is about 93%. That is more than 20% greater than the chances Hillary Clinton had of winning the election. Along the same vein, Hillary's chances were also lower than NBA's overall free throw percentage - 76.5% .
Silver's models also predicted which states are likely to swing the elections. Notice the "Blue Wall" states being high on the list. Pennsylvania, Michigan, and Wisconsin are 2nd 3rd and 7th on the list -
Both the most consequential and the least consequential events in our life are not deterministic. We live in a probabilistic world and we need to stop thinking deterministically about how things are going to turn out. Yes, the polls were inaccurate, especially in Michigan and Wisconsin, but they still provided us with enough of a trend as to say that this was not a sure thing. There was better than 1 out 4 chance of Trump moving into the White House.