"Long ago, I made a mistake as Lady's caretaker. An evil diesel found Lady and threatened to destroy her. he chased her, used up all her coal, then he crashed her. I tried my best to fix her up. But I've never been able to...make up for the mistake I made."
Muffle Mountain is the mountain Burnett Stone hid in for many years to try to repair Lady from her accident caused by Diesel 10. He lost all hope because of feeling guilty of Lady's disorder and losing his wife.