Big, there is a difference between being wrong and lying.
Have someone stuff your stocking with "Legacy Of Ashes", by Tim Weiner if you want to read a history of the CIA's success (or failure) in predicting events in foreign countries.
You can't believe how often our spooks have said "No way there will be an uprising" in the morning, only to have an uprising occur in the afternoon. Same thing with their appraisals of nuclear weapons, etc... It's hard to believe how inaccurate our information is at any one time, and the President and his cabinet have to sort through massive amounts of white noise.