Hm...
Polls in the US were pretty much on the mark except for certain states that (gasp) ended up flipping the election. In fact, Nate Silver warned there was a good chance this would happen because there was little to no polling in those states as they were considered "solid blue". In fact, the "winning" percentage in all of these were dangerously close to the margin of error.
The polls themselves might have flipped the election as well. Everyone took for granted that the states showing up as blue would remain blue, thus the "Bernie or Bust" crowd felt they could go third party or simply stay home. Which is also what happened during Brexit.
Lesson learned in 2016: Your vote matters. Don't skip it.
Biting the hand that feeds IT
