Shame will light a fire under you better than any desire. It isn't desire that gets someone to train like an animal. It isn't desire that deadlifts 900 lbs. It isn't desire that gets someone in the boxing ring and kills opponents left and right. It is the revenge of shame.
A bully kicked sand in your face.
Everyone laughed at your frail body.
The love of your life cheated on you.
The jock punched you and everyone laughed at you.
Your stepdad beat you up.
Everyone saw you cry.
They showed your cowardice to the world.
You let these things motivate you. You say to yourself “That will never happen again” and you mean it. You mean it every bit as much as you mean to breathe air and eat food.