In your story, does your character have to achieve his wants no matter what? Have you raised the stakes so high that he will struggle because the wants is so important to him?

Your characters desire has to be pretty important to him because thats what will motivate him in your story. When goals are conjured up from a whim, they are not powerful enough to sustain the characters actions.

Example

Your character is a doctor whos searching to find a cure for a particular disease.

What is motivating him to find the cure?

His child is dying from that disease.

So the stakes are pretty high for this character. He has to achieve his wants no matter what.