How did the life of knights and nobles demonstrate the importance of warfare in the middle ages?

In the middle ages, Europe is in perpetual warfare. Many Lords live in fortresses to protect themselves against enemies or allies alike. It is an age of no life assurance unless you are protected by strong vassals. Vassals are people in a subordinate position to another in exchange of land and favor.

The life of knights and nobles demonstrate the importance of warfare in the middle ages by conducting rigorous military trainings among themselves, by enlisting children to military services until they become fit for military purposes, by living in fortresses, by maintaing close allegiances, by having vassals to protect them in trying times, and by sensationalizing warfare and making it seem acceptable by justifying it as a means of survival but in reality, it's just the nobles who are truly in conflict themselves, vassal lords just find themselves in wars if their pledged lords found themselves in conflict.