Human nature inclines us to ignore indefiniteness, to underestimate it, or to hide it behind explanations, theories and absurdly small probabilities. When Richard P. Feynman was preparing an assessment of the Challenger space shuttle accident of 1986, he asked engineers and managers from NASA, "How high is the probability of such an accident occurring?" While the engineers would have expected a probability of around 1/100, the managers estimated it to be 1/100,000—a value that is obviously much too small. This absurdly small number would mean that a manned rocket could be launched into space once every day for 300 years without an accident ever occurring.