A student, Mohamed Bouazizi, is selling vegetables in Tunis to support his family. A policewoman complains that he doesn't have the proper permit. In the argument, she slaps him. He is humiliated and sets himself on fire. This in turn sets many Arab countries on fire.
Many have complained that the U.S. with its vast intelligence network didn't foresee this. Consider that many didn't foresee the fall of the Czar of Russia. Consider that Winston Churchill said in the 1920s that he thought war with Japan was impossible.
Other than knowing that kowtowing to dictators is itself playing with fire, I won't pretend to judge the intelligence community. I'll let you read some short analyses by other commentators. See "Why Didn't the U.S. Foresee the Arab Revolts?", Room for Debate, New York Times, 2011-02-24.