no of course not!
a great essay can contrast ideas effectively, which would probably demonstrate a different, or even greater understanding of the concept of journeys.
Perhaps you may need to find something that may tie them together in a very general way. For example, I had to contrast some cheesy happy journey where it makes them a better person in the end, with a Frankenstein the novel, whom obviously didn't have a very happy ending. Contrasting these, I tied them up by saying that the journeys undertaken, nevertheless created meaning for not only themselves, but for the reader by what it means to them... esp in a scientific way, ie in the book On Giant Shoulders by Melvin Bragg, a lot of scientists started a theory, never to prove them. Although the journey is a fairly "negative" or "incomplete" one, the journey is still taken, and has led other scientists to take on board the journey of discovery...
But anyway, enough of that, I don't wanna turn this into an essay, but its okay to contrast and use different texts that "aren't linkable".