Also climbing on The Sharp end. In the early days of climbing (1880's - 1940's), there was not way to secure the leader to the rock. He would tie a hawser rope around his waist and his seconds (the people climbing after him) would be tied to the other end of the rope. If the leader fell it potentially fatal for the entire party. The term "the leader must not fall" came into existence.

Over time much climbing terms was invented to help secure the leader against a fall. Some modern trad climbs have poor gear and if the leader falls he may well take his second with him. Guides to these climbs usually contain that old piece of advice "the leader must not fall"