I have a minor sideline in collecting examples of how bad we are at forecasting even the relatively near future. Brad DeLong provides a wonderful instance. He discusses a 1928 book, Republican Germany: An Economic and Political Survey.
“Writing in 1928, five years before Hitler was to take power and destroy the German Republic, and Adolf Hitler is simply not a big deal to two people writing a political and economic survey of Germany. Were Quigley and Clark obtuse? Not at all. Hitler was an unimportant part of the political fringe in Germany in 1928.
“In May 1928 Germany held elections for its legislature, the Reichstag. The Nazis won 2.6% of the vote: they were part of a fringe of small parties with more-or-less impractical and nutty programs that together drew off some twelve percent of the vote from the established parties on the right-left spectrum.”