Indomitable Spirit is the fifth tenet of Taekwondo, and it is the culmination of the first four: Courtesy, Integrity, Perseverance, and Self-Control. It is a trait of a person who will never give up and cannot be overcome. It is the complete resistance of defeat. It is spirit of undying courage and determination.
A person with indomitable spirit is not just concerned with themselves, however. A core aspect of indomitable spirit is a deep commitment to justice. Once you have mastered the ability to defend yourself as a martial artist, indomitable spirit will strive to defend those who are susceptible to abuse.
This is not an easy concept for children and the young. Indomitable spirit is really for adults, because it requires the wisdom that comes with age, experience and responsibity.
There are many stories of people facing overwhelming odds and chosing to face danger on behalf of others. People who run toward danger, such as military, police or firemen, are examples of indomitable spirit. It is the outward expression of bravery and courage that a martial artist should ultimately be ready for.