Why is outdoor bouldering so hard?

 There are many people who derive fun and satisfaction from bouldering, which essentially involves climbing up—or jumping over—steep rock formations with or without hand grab surface-spacing —and then more satisfaction is gained from leapfrogging from one rock to another WITHOUT there being visibly seen footholds anywhere in sight. Yet such elevated sense of achievement can never be attained without plenty of hard training and GUTS, for if there is just one slight slip by a margin of no more than two inches, possibly FATAL accidents could occur…