Why did Hillary lose?

Hillary Clinton was ahead in the polls before, which is the problem of sample error in statistics. When the number of samples is insufficient, the preferences of the participants and the final results may be different (see the preface of the fifth edition of Principles of Statistics for details, which makes it clear).

Hillary's supporters are mostly white-collar workers and middle class, and their enthusiasm for surfing the Internet and participating in polls is relatively high. So in the initial survey, Hillary was in the lead, and the votes of the States in the future basically met this point.

However, many blue-collar workers hope to gain dignity through work. They don't care what America does overseas. They are concerned about how to find a job. They look down on illegal immigrants who get something for nothing.

In this case, Trop's nationalist remarks and the economic policy of the return of manufacturing industry are just what he wants.

So in the general election, they voted for Trump.

In marketing, Hillary chose the wrong target audience.