( CNN ) -- Horrific events , such as the massacre in Aurora , can be catalysts for social and political change . Sometimes it seems that they 're the only catalyst ; recall how drastically our policies toward terrorism changed after 9/11 despite how moribund they were before . The problem is that fear can cloud our reasoning , causing us to overreact and to overly focus on the specifics . And the key is to steer our desire for change in that time of fear . Our brains are n't very good at probability and risk analysis . We tend to exaggerate spectacular , strange and rare events , and downplay ordinary , familiar and common ones . We think rare risks are more common than they are . We fear them more than probability indicates we should . There is a lot of psychological research that tries to explain this , but one of the key findings is this : People tend to base risk analysis more on stories than on data . Stories engage us at a much more visceral level , especially stories that are vivid , exciting or personally involving . When it 's not 'only a movie ' If a friend tells you about getting mugged in a foreign country , that story is more likely to affect how safe you feel traveling to that country than reading a page of abstract crime statistics will . Novelty plus dread plus a good story equals overreaction . And who are the major storytellers these days ? Television and the Internet . So when news programs and sites endlessly repeat the story from Aurora , with interviews with those in the theater , interviews with the families and commentary by anyone who has a point to make , we start to think this is something to fear , rather than a rare event that almost never happens and is n't worth worrying about . In other words , reading five stories about the same event feels somewhat like five separate events , and that skews our perceptions . We see the effects of this all the time . It 's strangers by whom we fear being murdered , kidnapped , raped and assaulted , when it 's far more likely that any perpetrator of such offenses is a relative or a friend . We worry about airplane crashes and rampaging shooters instead of automobile crashes and domestic violence -- both of which are far more common and far , far more deadly . Our greatest recent overreaction to a rare event was our response to the terrorist attacks of 9/11 . I remember then-Attorney General John Ashcroft giving a speech in Minnesota -- where I live -- in 2003 in which he claimed that the fact there were no new terrorist attacks since 9/11 was proof that his policies were working . I remember thinking : `` There were no terrorist attacks in the two years preceding 9/11 , and you did n't have any policies . What does that prove ? '' What it proves is that terrorist attacks are very rare , and perhaps our national response was n't worth the enormous expense , loss of liberty , attacks on our Constitution and damage to our credibility on the world stage . Still , overreacting was the natural thing for us to do . Yes , it was security theater and not real security , but it made many of us feel safer . The rarity of events such as the Aurora massacre does n't mean we should ignore any lessons it might teach us . Because people overreact to rare events , they 're useful catalysts for social introspection and policy change . The key here is to focus not on the details of the particular event but on the broader issues common to all similar events . Opinion : Average Americans do n't need assault weapons . Installing metal detectors at movie theaters does n't make sense -- there 's no reason to think the next crazy gunman will choose a movie theater as his venue , and how effectively would a metal detector deter a lone gunman anyway ? -- but understanding the reasons why the United States has so many gun deaths compared with other countries does . The particular motivations of alleged killer James Holmes are n't relevant -- the next gunman will have different motivations -- but the general state of mental health care in the United States is . Even with this , the most important lesson of the Aurora massacre is how rare these events actually are . Our brains are primed to believe that movie theaters are more dangerous than they used to be , but they 're not . The riskiest part of the evening is still the car ride to and from the movie theater , and even that 's very safe . But wear a seat belt all the same . The opinions expressed in this commentary are solely those of Bruce Schneier .
Bruce Schneier : When horrific events happen , we look for patterns . He says people are n't good about understanding probabilities and often exaggerate risks . Obama : After Katrina , policies were implemented that caused enormous expense and damage . He says much can be learned if we look at patterns among many events .