Five years ago, if you'd told me that one day I'd be (-------), I'd have said you were crazy.
Can you fill in that blank? Are you doing something today that you never would have considered doing a long, or even short time ago? If so, you have lots in common with traditional screenplay heroes, who must pull a psychological about-face by the end of the story. They must vanquish both the enemy without and within, or in the case of a tragic/nihilistic story, execute a swan dive into ruin.
This character arc can be difficult to write into your script, because sometimes you simply have a cool idea for a movie that doesn't rest on a character metamorphosis. Many high-concept movies are just whizbang fun; they're not trying to change the world. But without some character change, the story can seem emotionally hollow, so filmmakers typically do one of two things: Either add more explosions, or superimpose an imbecilic character arc.
Sometimes they get lucky and somebody writes in a plausible, moving arc, but more often we get patronizing character reversals such as TOP GUN's infamous "never leave your wingman" message, which boiled down to "there's no 'I' in 'team'", which boiled down to "join the navy". More on-the-nose character arcs are the workaholic who decides that family is more important, the city slicker who abandons the flash of urban life for rural bliss, or the good guy who commits a single sexual infidelity (has his cake) and then must manfully vanquish the sexy-crazy temptress (eats it, too).
Like I said, though, sometimes we get lucky. Take RAIDERS OF THE LOST ARK, for example. Who says great action and great characterization can't fit on the same page? Indiana Jones's driving purpose in life is to discover artifacts, to see, touch, and take. By the end of the story, he decides to shut his eyes rather than look upon the innards of the Lost Ark of The Covenant. He's come to realize that the Ark is not just a mundane item like Belloq's watch, buried in the sand for thousands of years. The Ark is sacred, and dangerous. Not only that, but Indy also has learned a new respect for the living. Marion isn't a disposable diversion now; she's a woman with whom he has reconciled and grown to love.
Similarly, UNFORGIVEN charts a reverse course for hero Munny, who starts out as a reformed widower and father who agrees to punish a vicious man for much-needed cash. By the time his course intersects with his nemesis however, he's fully recovered his abandoned persona: a hard-drinking killer who fights evil with evil. The reward money is the last thing on his mind by the time he brings the bottle of whiskey to his lips after all those long, domesticated years.
Good character arcs need to be submerged somewhat, and most of the bald reversals could be made better with a little tweaking. Even clich?s can work if a writer takes the time to present the changes in a fluid, honest way. For example, AN OFFICER AND A GENTLEMAN has basically the same hero arc as TOP GUN. The former film succeeds artistically because it isn't afraid to make its hero quite unlikable in both the first and second acts. It's only in the third act that Zack's care for his best friend starts breaking down the wall he's built up around himself. TOP GUN insisted on making its hero likeable or macho in every frame.
What does your hero do in the third act that he wouldn't have dreamed of doing in the first? Look for ways to enrich the journey for him, be it a rise from the bottom or a fall from the top. It's not just about making a character do an abrupt 180 degree turn; it's about revealing something that was in the character all along and pulling it to the surface. The writer has to keep lifting away the veils and show the audience who the person really is.