The polls are accurate. The polls, however, do not measure public opinion in the same way elections are held. They would have to sample every single riding to give a more accurate picture of the election outcome. That would be prohibitively expensive, so they make inferences from popular opinion and extrapolate based on the characteristics of the populations in each riding. Most of the time they don't take that second step and just report on popular opinion, sometimes adjusted for voting intention and past voting behavior in relation to demographic characteristics. Another challenge with polling is that you're dealing with human beings. We are rational creatures, which means the publication of results from polls leads people to think about and react to them, thereby changing the results almost immediately upon publication. Nevertheless, the polls that we have a far better predictors than drawing names out of a hat or flipping a coin. The Trump and Hillary polls is also a perfect example that the electoral system does not work based on the will of the voters. The polls were very accurate. In fact, Hillary Clinton did beat Donal Trump in the election, based on the number of votes each received. That's, however, not how you get elected in the United States. That's not how a premier is elected in Ontario either. You only need a plurality of votes across various sub-divisions of the population. But at the end of the day when you aggregate the vote, ignoring ridings and "electoral college" the polls are very close.