Idiom: It's not the size of the man in the fight, it's the size of the fight in the man

What does 'It's not the size of the man in the fight, it's the size of the fight in the man' mean?

This idiom means that determination is often more important than size, strength, or ability.  ('It's not the size of the dog in the fight, it's the size of the fight in the dog.' is also used.)

See also: