Character Development vs. Acting Out-of-Character

What is the difference between character development and a character acting out of character?

Acting out of character is when a character suddenly shows a trait without any warning or explanation.

Example: a cowardly character running away from every single battle in the story only to show up at the big climax and ends up being incredibly brave.

Character development is when said cowardly character learns how to be brave before the climax.

Just like plot, characters must be consistent. In order for them to go from cowardly to courageous, there must be a progression throughout the plot of the character learning to be courageous, so that when the big battle comes, it won’t come as abrupt for the character to stay and fight.

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