You can't always get what you want
But if you try sometimes, well, you might find
You get what you need
— Rolling Stone
In his book The Anatomy of Story, John Truby says that a character has both desire and need.
Desire drives the story. It is:
what your hero wants in the story, his particular goal.
But your character also has an even deeper want: their need. Need is:
what the hero must fulfill within himself in order to have a better life. It usually involves overcoming his weaknesses and changing, or growing, in some way.
This need develops from your character’s weakness, which occurs because:
something is missing within him that is so profound, it is ruining his life.
For Truby, desire and need are “intimately connected.” The needs of a character will drive their desires.
A character may need to protect his family, so he has the desire to threaten the villain when they come too close.