Every character has one. Whether it’s an older friend or relative, there’s someone who possesses wisdom or power that the protagonist just doesn’t quite have yet.
Think of your favorite books and movies. Who was the character that aided the protagonist? How did they do so?
The previous exercises should be done with the intent of answering one question: how should they best support the protagonists’ outer goal?
If it’s possible for them to understand what the inner conflict is for the protagonist, even better.
Don’t rely too hard on the supporting characters, but DO make sure you find that balance. They exist for a reason – they are devices for you to use… while also needing to be important and human.
It’s a tough job, being a writer.