Every year in Pamplona , Spain , hundreds of people run alongside 1300 - pound ( 600 - kilo ) bulls , just for the fun of it . And every year at least a few of these people are injured , some seriously . yet this does not stop people from participating in the event . what is it that drives some people to embrace extreme risks , while the rest of us run to the safety of the sidelines? lester keller , a long time coach and sports - psychology coordinator for the U.S. ski and snowboard association , says that not everyone has the mental character to excel in dangerous pursuits.