Familiar text is a linear sequence of parts.
Authors work hard to create a clear and convincing sequence of narrative, exposition, or argument.
It is not easy to decide how to order the text, and the best rhetorical order may not be the order of dependence of the ideas involved. A hypertext, by contrast, is a web of pieces of text. The individual units of the web may be sentences or chapters, but what is crucial is that they do not relate to one another in any unique sequence. The author cannot control which links the reader will follow, and in some systems the reader can create new units and links so that the web changes and grows. The structures of ideas are not sequential.