Bushido

Bushido meaning "way of the warrior," is a Japanese code of conduct and a way of life, loosely analogous to the European concept of chivalry, Bushido is the code of moral principles which the samurai were required or instructed to observe.
Bushido expanded and formalized the earlier code of the samurai, and stressed frugality, loyalty, mastery of martial arts, and honor to the death. Under the Bushido ideal, if a samurai failed to uphold his honor he could regain it by performing seppuku (ritual suicide).

So here come the question what is that thing that require the samurai to kill them-self if they have to and why are they obliged to live by it if it require them to kill them-self in certain situations since anyone sane enough will say this is not a way of life if it get you to kill your-self for it and what is it for you if you live by that code? I can't say that the answer for that is simple to undersatnd so the answer for this question is in one word it is "FAITH" I don't want to go through a religious stuff ( shinto or Buddhist) I just want to make my point that they believed in that this way of life is how a true warrior should liveand die.
Here are Seven virtues associated with bushido:

Gi – Rectitude
Yū – Courage
Jin – Benevolence
Rei – Respect
Shin– Honesty
Meiyo – Honor
Chū – Loyalty

Others that are sometimes added to these:

Kō - Filial piety
Chi - Wisdom
Tei - Care for the aged

well it is very obvious that these virtues are pretty impressive even for a saint so now it is more clear why the samurai believed in Bushido since it represent everything that a samurai should be endowed with so to hold these qualities and defend them is more important than life it-self for the samurai because these qualities define the samurai and without them they are nothing more than ordinary brawlers with no ethics and principles so in reality by defending these virtues the samurai defend their isism and who they are and isn't that indeed something worthy to give your life for...

I'll end my post by the word of the great Samurai Torii Mototada when he chose to stay behind in his master (Tokugawa Ieyasu) castle to provid him more time to escape.
" It is not the Way of the Warrior to be shamed and avoid death even under circumstances that are not particularly important.....For myself, I am resolved to make a stand within the castle and to die a quick death. It would not take much trouble to break through a part of their numbers and escape, no matter how many tens of thousands of horsemen approached for the attack or by how many columns we were surrounded. But that is not the true meaning of being a warrior, and it would be difficult to account as loyalty. Rather, I will stand off the forces of the entire country here, and...die a resplendent death"