What does indomitable spirit mean in Tae Kwon Do?

The Word indomitable means "unconquerable," or impossible to defeat or frighten. The "spirit" is the person's core being, their will power, cheerful & positive attitude, and desire to succeed. Having an "indomitable spirit" means that your fortitude, enthusiasm, and moral character are never diminished regardless of the hardships and adversities you face. Your determination to prevail is never vanquished, even in the face of what appears to be insurmountable odds, or seemingly overwhelming opponents.

This concept is reflected in the following popular saying:

"It is not so much the size of the dog in the fight, as the size of the fight in the dog."