Intelligence, like warfare, is not a science but an art. If a science at all, it is certainly far from an exact science. It is an intellectual endeavour which requires much training, common sense, experience, team work, technological expertise and the ability to communicate the product to the user, to name but a few of the basic requirements. It also requires intellectual bravery to give the result of the intelligence assessments to the user, without the tendency to be vague, so as to excuse faulty intelligence predictions in the future. It remains a human endeavour prone to mistakes. Intelligence failures are thus to be expected, but good tradecraft, and above all sound analysis, can lead to success. In this article, the concept of intelligence and the underlying reasons for intelligence failures are discussed, and subsequently applied to a number of case studies involving some apparent intelligence failures.