Forecasts that come true are easily forgotten. The prophet who live to see his prediction falsified by reality wishes it would slide into oblivion. But precisely these statements are echoed hilariously because, with superior hindsight, we know better than the famous person who made the prediction.

There are several interesting books about the phenomenon. Steven Schnaars’Megamistakes is one of the nicest. Several websites also carry nice collections of bad forecasts, e.g. this Wikipedia page.
Here’s a collection of my favourite forecasts that are off the mark.