How we cite our quotes: (Page.Paragraph)
Quote #1
This first stage of the mythological journey—which we have designated the "call to adventure" —signifies that destiny has summoned the hero and transferred his spiritual center of gravity from within the pale of his society to a zone unknown. (47.4)
This is definitely the sign that destiny is calling the shots, at least early on. Fate selects the hero, and the hero can only react to the summons. Free will only enters the picture if the hero refuses the call…and even then, fate has some nasty ways to get the hero back in line.
Quote #2
The hero can go forth of his own volition to accomplish the adventure, as did Theseus when he arrived in his father's city, Athens, and heard the horrible history of the Minotaur; or he may be carried or sent abroad by some benign or malignant agent, as was Odysseus, driven about the Mediterranean by the winds of the angered god, Poseidon. (47.4)
Once the call goes up, the hero can sometimes accept it of his own free will, in which case he or she's acting in concert with fate. Other times, fate just grabs the hero and carries him or her off, which puts the hero in a more adversarial position with fate.
Quote #3
Often in actual life, and not infrequently in the myths and popular tales, we encounter the dull case of the call unanswered; for it is always possible to turn the ear to other interests. (48.3)
There's always free will involved, especially here, when the adventure is just starting. The irony is that exercising free will by refusing the call only hurts the hero, not the rest of the universe.
Quote #4
The hero to whom such a helper appears is typically one who has responded to the call. The call, in fact, was the first announcement of the approach of this initiatory priest. But even to those who apparently have hardened their hearts the supernatural guardian may appear; for, as we have seen: "Well able is Allah to save." (67.1)
Here's that balance again: destiny is going to be served no matter what, but the hero's choices can make the path smoother and easier.
Quote #5
To move toward destiny is like eternity. To know eternity is enlightenment, and not to recognize eternity brings disorder and evil. (175.2)
The whole point of the Hero's Journey is to put the hero's free will in sync with the universe, and thus enjoy the enlightenment it brings. It's not supposed to be a struggle between man and fate, but a way of putting man on the same page as fate.
Quote #6
The irony, of course, lies in the fact that, whereas the hero who has won the favor of the god may beg for the boon of perfect illumination, what he generally seeks are longer years to live, weapons with which to slay his neighbor, or the health of his child. (175.5)
Another case where the hero gets to exercise free will…but note Campbell's tone: choosing poorly means staying mired in petty concerns instead of embracing destiny. That always brings pain.
Quote #7
The hero may have to be brought back from his supernatural adventure by assistance from without. That is to say, the world may have to come and get him. (192.1)
Fate can always lend a hand from time to time if the hero needs it. Just so long as the hero is moving in the direction that fate desires.
Quote #8
Perhaps the most eloquent possible symbol of this mystery is that of the god crucified, the god offered, "himself to himself.'" (241.2)
The notion of choosing to make a sacrifice like that only illustrates the book's central point: we're all connected to the universe and our choices either show us that connection or drive us further away from it.
Quote #9
The cosmogonic cycle is now to be carried forward, therefore, not by the gods, who have become invisible, but by the heroes, more or less human in character, through whom the world destiny is realized. (291.2)
That's a pretty profound thing. Heroes become the agents of destiny, though they are still human, which means they mess up sometimes and have to get back on track. But without them, destiny really serves no purpose. It needs us and our free will to fulfill its purpose.
Quote #10
This accords with the view that herohood is predestined, rather than simply achieved, and opens the problem of the relationship of biography to character (294.3)
Here's the problem of shining steel rails, aka, "destiny calls the shots no matter what." It denies the human experience, where we grow and learn and gradually become wiser. Without that process, which includes us making choices and living with the consequences, we could lose the purpose of being human.