The Question and Answer section for Thus Spoke Zarathustra is a great resource to ask questions, find answers, and discuss the novel.
An abyss has no bottom so I think it means the person keeps falling.
Zarathustra says that the world revolves around the Overman because he is the ideal human being. The Overman is superhuman, has the ability to lead and control those who are unable or unwilling to care for themselves, concentrates on pleasuring...
Man is the presence that totters over the abyss..... like a tight-rope walker. He will either cross the rope and realize his full potential..... or he will fall.