In order to secure a whale after it is harpooned, a large hook must be inserted into it. In the case of the whale Stubb killed, this dangerous task fell to Queequeg, who had to stand atop the whale, while sharks snapped all around him. The only thing keeping Queequeg safe from plunging into the shark-infested waters was a rope tied around his waist, which was also tied around the waist of Ishmael, who stood on the deck. This rope was called the “monkey-rope." The idea behind the monkey-rope is that, if one person should fall, the other would also perish. Hence, the two ship-mates had to help one another. Their survival depended on it.
In this situation, Ishmael sees a profound philosophical significance: “So strongly and metaphysically did I conceive of my situation then, that while earnestly watching his motions, I seemed distinctly to perceive that my own individuality was now merged into a joint stock company of two…I saw that this situation of mine was the precise situation of every mortal that breathes.” Being literally connected to Queequeg by a rope helped Ishmael to see that no one is truly an island. We are all connected to others for our happiness and our survival. This is perhaps a mild critique of the very American idea of the “rugged individual” and self-determination. Though we may like to think of ourselves as totally self-sufficient, the truth is that our fates are often entertwined with others.