Character is most deeply revealed in moments of decision that produce change.
I think this is a principle of life, too.
Change can occur when the character makes a decision to do something different than what they’ve been doing before (like seizing control of their destiny, for example). Or the change can take place in the audience, when they recognize something they hadn’t known about the character, so that they change their attitude towards the character or their conception of them. Aristotle called this “Anagnorisis,” Notice that the change in the character can take place simultaneously with the audience. There are significant examples of this in Casablanca, Citizen Kane, The Godfather, and, Apocalypse Now, to name just a few.If a character comes into a saloon and engages the bad guy in a gun fight, we might say it was a good scene, but that’s because gunfights, like car chases, dogfights in space, and other visualizations of physical actions are inherently engaging. But, very often in modern films, character development ceases during action sequences; in fact, in many modern films, it ceases after the first twenty minutes.
A good proportion of the most memorable films revolve around the question that is explicit in Lawrence of Arabia and Citizen Kane: “WHO ARE YOU?” The first place to look for the answer to that question is in scenes where the character makes a decision. In a good many of them, the decision revolves around an ethical question.
There is no such thing as a great character – there are only great character relationships. Great characters, therefore, are the result of great scenes.
What I have just written about the importance of ethical decisions applies to scenes as well as characters.