Ross Pomeroy reviews research on the subject:
In 1987, psychologist and risk perception expert Paul Slovic skillfully summarized in the journal Science how we calculate risk. In general, humans tend to be wary and apprehensive of risks that are uncontrollable, potentially fatal, possibly catastrophic, and relatively unknown.
The danger of terrorism put in perspective:
In the last decade, you’d be hard-pressed to go one day without hearing about [terrorism]. However, as Reason‘s Ronald Bailey wrote in 2011, an American’s chances of being killed by a terrorist are approximately one in 20 million. Heck, even if all of the thwarted terrorist attacks over the last 10 years were carried out, that still would translate to a risk of one in 1.7 million. Compare that to an infinitely more dangerous activity you may undertake every morning: climbing into a car. The annual risk of dying in a motor vehicle crash is one in 19,000.