To check if the warrior is capable of handling pressure as well as worthy enough to lead the soldier in the war, there are several requirements. Some of them are necessary because on the battlefield, you are not only responsible for your life but the life of all soldiers behind him.
The warriors and Captain had intertwined fate in the war and very few instances are seen where Captain comes back after his whole regiment is killed. They prefer to die with their men on the field than to come back alive. This kind of loyalty as well as the connection is what makes Captain capable enough to lead the soldiers. Because they are literally handing their lives in the hands of him when they unite their energy.