People who want to know the future have many tools. There are crystal balls, fortune cookies, horoscopes, and just a bit more credible, public opinion polls. The 2020 election featured a spectacular failure of the polling industry.
RealClearPolitics catalogues all major (non-candidate) polls. They also average the results of all recent polls, which effectively increases the sample size and reduces the margin of error. Their national polling average was Biden +7.2, while the popular vote was Biden +4.5, an error of 2.7%. The results in many state polls were even worse. In Ohio, the error favored Biden by 7.2%. In Iowa, it was 6.2%. In Wisconsin, it was 6%. Overall, Trump outperformed the polls in 33 states. Curiously, Biden did overperform the polls in a few states, including Minnesota.