This was one of the first things I learnt in my novel class back in 2009. My teacher, Ray Mooney, told us many times. “You must set a character up and then put them to the test.”
This is something I always try to remember when I’m writing up a scene or thinking about plot and characters.
Basically it means you put a character in a situation where they have to make a choice and that choice gives the reader insight into who they are.
So you set the character up in a situation like their best friend has been kidnapped, he has a chance to try to save them, but it could mean they will be caught also.
The character has two choices: save their friend or run away. The choice they make will show the reader your character is either brave and courageous or cowardly and selfish.
This is a technique to live by in my opinion. It is a great way to reveal things about your character without having to say “Bob was a courageous man who would risk his life to save anyone.”
It’s just so much better being able to see the character in action.