Focus your energies on commonalities between threats

In Rare Risk and Overreactions Bruce Schneier writes, "If you want to do something that makes security sense, figure out what's common among a bunch of rare events, and concentrate your countermeasures there. Focus on the general risk of terrorism, and not the specific threat of airplane bombings using liquid explosives. Focus on the general risk of troubled young adults, and not the specific threat of a lone gunman wandering around a college campus. Ignore the movie-plot threats, and concentrate on the real risks."