Or the Iraq intelligence operation, which led to the Iraq war and a lot of the present-day instability in the region. There was wrong intelligence that was believed-in, and right intelligence (claiming there were no massive stockpiles of WMDs) that was dismissed [1][2].
[1]: https://www.telegraph.co.uk/news/worldnews/middleeast/iraq/9... [2]: https://www.washingtonpost.com/news/fact-checker/wp/2016/12/...