@miriam98 - As long as humans are involved in ferreting out intelligence, mistakes will be made.
Enemies of state are smarter than we think many times. Sometimes they bluff, and fake out our analysts. They make us believe what they know we want to believe, perhaps to advance other aims that they may have – political or strategic aims.
It’s an imprecise science, but we just have to learn from our mistakes and move on. People will never be perfect.