Bruce Sterling Schneier has a good article on the dangers of risk analysis when estimating software projects – and, by extension, estimating the risk of terrorist attacks.

It is the everyday risks that kill you – largely because the effect is delayed and the risk itself not very visible. I seem to remember someone proposing that the way to get responsible driving would be not to increase the safety level of the car, but instead decrease it – for instance by outlawing seat belts and mandating a four inch sharp metal spike placed in the middle of the steering wheel.

If too much imagination can make us overly risk-averse, a heavy dose of reality might have the opposite effect.