The Hero's Journey, as explained by Joseph Campbell, is the basic framework of many myths. It chronicles the stages that a person/character/youngster goes through to become something more. It has been used, quite successfully, as a framework for evaluating and directing lives.
In general, an ordinary person leading an ordinary life gets called to a great adventure and rejects it. The stakes are raised (sometimes many times) until the hero accepts, then he meets a teacher, a mentor, who shows him something about how to survive what he is about to face. The hero then faces the first challenge and commits to taking it on. Maybe wins, maybe not. Maybe the first challenge was an illusion... but the hero is committed and keeps at it until he passes this test, only to find out that this is nothing, a prelude, a taste.
He is changed, though, and begins in ernest to both become what he is destined to be and come to terms with it. He will make friends and enemies, gather allies and wisdom and take and pass many tests.
Then he will face darkness, the true challenge. Everything will be on the line, not just his life, but his identity. He will have to face the hardest temptation of all, the temptation to quit, to take the laurels he has won and go home. This is the 'why' phase, the place and time of insight. It will shatter illusions about what the hero is to himself and to the universe.
Beyond that is the gift, the goal, the chalice. In myth, the grail or the Medusa's head or... many things. In life it is usually an insight and depth of understanding.
There are many many variations, many archetypes one may stumble across. It can be repeated over and over as the Hero tries to settle down and is called for new problems.
Because it is couched in the language of myth, people miss how often they have lived this. Imagine a blue collar high-school kid who, during an assembly hears about college. Nah, he says, I'm not smart enough or rich enough. He hears the girl he has had a crush on for years is going to State. Still, he rejects. (Maybe more piles on, he is told of a career he would love that requires college or an ailing grandparent whispers that she wants one member of the family to attend college before she dies.)
So he decides to apply and contacts the school counselor (who may encourage or discourage, may be the first mentor or the first test). You see the tests and the challenges linig up? Taking grades seriously for the first time. The SATs. Applications and interviews. The mentors, allies and enemies- the roommate who was always going to college and knows what to expect. The RA who recognizes the kid is lost at college, the upperclassman asshole. Each challenge, each test. Each final exam. Each serious date. All the times the poor kid though 'I can't do this, I'm not cut out for this...' and talks himself out of giving up. Each extraordinary teacher or complete ogre until... finals and a thesis. Do we all know someone who worked on his thesis for years? Or someone who never completed it, swallowed by the big challenge?
And the reward, the diploma which does change everything about the former blue-collar highschool kid, who now sees a bigger world and has prospects for a completely different life.
Then the career becomes the next journey...
Do you see this? Like evolution, it is everywhere if you open your eyes. You have lived this a dozen times in big and small ways. Every decision you have made that was truly big enough to change you has followed this pattern. Maybe not all the steps and maybe not in the exact order. Maybe you 'met the temptress' (one of the variations) and maybe you 'met the Goddess'. Maybe you journeyed mostly alone. But this is not new territory for you, just the images have changed.