According to cognitive linguists (like George Lakoff, for instance), people tend to conceptualize metaphorically certain aspects of their existence. Cognitive scholars maintain that metaphors (concepts structured in terms of other concepts) are not merely a figure of speech, a rhetorical trope, but the property of our brain, a way by which it perceives and makes sense of the world. .
I guess the concept of "journey" is one of the basic concepts by which we think of the surrounding reality. We tend to apply this vehicle (figurative term) to all sorts of tenors (primary literary terms): to our various relationships, actions, experiences, to life itself. It is hard to think of something that could not be "figuratized" in terms of a journey, because it is indeed a universal, all-embracing concept. It implies purpose, progress, obstacles, layovers, perseverance and arrival - a pattern common to most non-static aspects of our existence. Everything that moves and changes is a journey in some respect.
Metaphorical expressions derived form the conceptual domain associated with "journey" abound in English (and surely in other languages as well): to be at a crossroads, to be lost, to have a bumpy ride, to move on in life, to set out to do something, to get over something unpleasant, to be over the hill - to name but a few. It must be very fascinating to try to discover the common ground, the correspondences between the source and target domains united in a metaphor: options are crossroads, indecision is disorientation, difficulties are bumps, etc.
Literature is a playground for thought, and we think figuratively. So the meaning of the journey metaphor in literature is central, I think. Each and every story starts, develops and ends. It transforms its characters from one spacio-temporal point to another. Thus essentially, each story tells a journey: either literal (physical) or metaphorical (spiritual).
