Giving a character their “character”

I feel like there are a million character flaws or undesirable traits out there, but what really brings a character's flaws to light for me is when they're faced with a particular challenge and are forced to feel something. It's how selfishness grows into narcissism, and envy turns to jealousy and hate.

When writers place emotional weight on a character, it always makes them so relatable, in my opinion. What is life without burdens? What moves us like anxiety? What puts a fire in a character's eyes like pressure?

It's what gives a character their "character."

How do they react to life's obstacles, how does it affect their journey, and what will come from it?

Will they make a wrong decision early, but learn a life lesson that reshapes the way they see the world? Or maybe they'll continue their behavior until they experience significant trauma.