First, any risk assessment carries uncertain claims about future events that cannot be accurately described or predicted. Second, only some risks can be selected for priority attention; those not addressed are sources of uncertainty. Third, specific decisions in risk management contain the uncertainty of false positives and false negatives. Fourth, risk-management technologies produce new uncertainties, some of which carry risks greater than those they were intended to control. Fifth, risk is reactive; and as people act on knowledge developed from risk assessment, they change the risk environment, which creates new uncertainties. Sixth, the complexity of risk-management systems can result in many and unexpected failures that occur simultaneously. Seventh, catastrophic failures produce the urge to address all potential threats through intensified surveillance, audit, and regulation. This increases system complexity, which carries more uncertainty. Eighth, risk managers who focus on security failures likely to bring lawsuits tend to focus more on operational risks that affect their organization's public reputation rather than on more serious threats to the company and its personnel. Ninth, excessive precaution escalates uncertainty and breeds fear, leading to risk-management measures that are at best misplaced, and at worst fuel new risks with catastrophic potential. Tenth, risk-management systems can restrict freedom, invade privacy, discriminate, and exclude populations. In the case of terrorism, costly attempts to eliminate inevitable uncertainties regarding terrorist threats can create the threat of harmful side effects, the neglect of other types of threats to public safety, and a diminishment in commitment to the values of human rights and overall quality of life. 25 references