...but in fact they are potential suicides. Fear of heights does not exist for them, they do not even know any instincts of self-preservation. Joking with death is just their favorite game. For example, climbing old rusty stairs on a 300 meters top without a safety net or running on the edge of a roof of a 40 storey building. They do it not for any sporting interest or records, they simply like to have fun together in extreme conditions.