People tend to think that events could have been easily predictable AFTER the outcome is clear. The certainty that people attribute to their predictions are much higher that it actually is.
This has the ability to distort memories of what we believed/the probability we assigned to the outcome before the event has occurred.
This effect is so powerful that many experts think that true analysis of any decision can be done only before you know the outcome.
Also know as "Knew-it-all-along" phenomena.