Taekwon-Do is a fighting art, and the ultimate test of one's competence is the ability to defend oneself in a fight. This test, however, should not be just a function of who is bigger, stronger, or faster, but rather a test of refined technique and skill in physical combat. To attain this high level of skill in Taekwon-Do requires great attention to the details of technique, theory, and attitude. Concentration on these areas of training and study ultimately results in proficiency for the dedicated martial artist. In this type of training, hardship is the anvil that forges moral character; with perseverance, self-control, and indomitable spirit as the hammer, improvement follows. This hardship has a way of teaching us the need for courtesy, integrity, and self-control by making progress more difficult without them. In a complex interaction of cause and effect, the perfection of martial arts skills is ultimately tied to the development of moral character, and developing these skills. Therefore, regardless of one's goal in martial arts, a well-balanced emphasis on the physical, intellectual, and moral aspects of training is essential.
-from 'History of Taekwon-Do Patterns' by Richard L. Mitchell

Courtesy - Ye Ui
Courtesy: Acting in ways that are well mannered (polite.)
Courtesy is the first of the five Tenets of Taekwon-Do. A student may wonder how he or she is learning courtesy while punching, blocking, kicking, performing patterns, practicing step-sparring and free sparring. The tenet of Courtesy is developed by learning and practicing etiquette, as described by General Choi. It can be said that courtesy is an unwritten regulation prescribed by ancient teachers of philosophy as a means to enlighten human beings while maintaining a harmonious society. Taekwon-Do students should attempt to practice the following elements of courtesy to build up their noble character and to conduct their training in an orderly manner as well:

1) To promote the spirit of mutual concessions
2) To be ashamed of one's vices, comtempting those of others
3) To be polite to one another
4) To encourage the sense of justice and humanity
5) To distinguish instructor from student, senior from junior, and elder from younger
6) To behave oneself according to etiquette
7) To respect others' possessions
8) To handle matters with fairness and sincerity
9) To refrain from giving or accepting any gift when in doubt

Integrigy - Yom Chi
In Taekwon-Do, the word integrity assumes a looser definition than the one usually presented in Webster's Dictionary. One must be able to define right and wrong and have the conscience, if wrong, to feel guilt. Listed are some examples where integrity is lacking:
1) The instructor who misrepresents himself and his art by presenting improper techniques to his students because of a lack of knowledge or apathy
2) The student who misrepresents himself by "fixing" breaking materials before demonstrations
3) The instructor who camouflages bad techniques with luxurious training halls and false flattery to his students
4) The student who requests rank from an instructor, or attempts to purchase it
5) The student who gains rank for ego purposes or the feeling of power
6) The instructor who teaches and promotes his art for materialistic gains
7) The student whose actions do not live up to his words
8) The student who feels ashamed to seek opinions from his juniors

Perseverence - In Nae
There is an old Oriental saying "Patience leads to virtue or merit." "One can make a peaceful home by being patient for 100 times." Certainly, happiness and prosperity are most likely brought to the patient person. To achieve something, whether it is a higher degree or the perfection of a technique, one must set his goal, then constantly persevere. Robert Bruce learned his lesson of perseverance from the persistant efforts of a lowly spider. It was this perseverance and tenaacity that finally enabled him to free Scotland in the fourteenth century. One of the most important secrets in becoming a leader of Taekwon-Do is to overcome every difficulty by perseverance.
Confucius said, "One who is impatient in trivial matters can seldom achieve success in matters of great importance."

Self-Control - Guk Gi
This tenet is extremely important inside and outside the dojang, whether conducting oneself in free sparring or in one's personal affairs. A loss of self-control in free sparring can prove disasterous to both student and opponent. An inability to live and work within one's capability or sphere is also a lack of self-control.
According to Lao-Tzu, "The term of stronger is the person who wins over oneself rather than someone else."

Indomitable Spirit - Baekjul Boolgool
"Here lie 300, who did their duty," a simple epitaph for one of the greatest acts of courage known to mankind. Although facing the superior forces of Xerxes, Leonidas and his 300 Spartans at Thermopylae showed the world the meaning of indomitable spirit. It is when a courageous person and his principles are pitted against overwhelming odds.
A serious student of Taekwon-Do will at all times be modest and honest. If confronted with injustice, he will deal with the belligerent without any fear or hesitation at all, with indomitable spirit, regardless of whosoever and however many the number may be.

Let us out do one another in being helpful and kind.

taken from the Encyclopedia of Taekwon-Do by General Choi Hong Hi