Flaws Every Day

We're always advising people to give their characters flaws. But why? Is it just so they'll be relatable and not perfect/boring?

That is a good reason, for sure.

Is it so you'll know how they're supposed to react in certain situations?
"I wrote in my notebook that Jenny is impatient. She oughtta start yelling and honking her horn at the traffic light!"

That's getting closer to it I think, but even more importantly, the flaws are important because they get in the way of what your character WANTS in the story, and NEEDS in their soul.

Recognizing and then learning to overcome their flaws IS the story, in a way. You have to know what your character wants more than anything (to be a fighter pilot, to be with the romantic partner of their dreams, to win the Uno championship, whatever).

And to have a deeper level, you need to know the NEED inside them as well - the need to grow up in some way, or to stop believing the lie they've been living with, or to heal the wound that's stopping them from being who they're supposed to be. The flaws are probably a result of the wound (or caused the wound in the first place, sometime in the past).

Then you give them the flaw - the big thing that's holding them back from getting what they need or what they want. The character might not even know it exists in the beginning of the story. They most likely don't. They'll learn!

Overcoming their inner flaws is what gives your stories real juice, and lifts the hearts of your readers.