We think that brothers are brothers, but in the language of the environment, this blood relationship is not placed in the supreme position. In fact, brothers are often separated and have their own lives, and intimate friends and right-hand men are as indispensable as a person's hands and feet. This rare fate between people is more intimate than blood.
Losing hands and feet means that the best friend has left himself, not only in life but also emotionally, so this situation is usually explained as death.