By comparing their pasts, the office workers can relate, and thus establish a basic good friendship with the others. The soldiers, on the other hand, train together for weeks at a time and experience something slightly different. Both soldiers have been 'pulled out' of their usual environments by means of some military draft, so they share only that as an experience. The rest evolves out of working together and knowing that each will have the other's life in his hands some day. As a result, both soldiers become each other's 'buddy', a synonym for good friend.
Ordeal is only one way to bring friends together, the other way is through competition.
Both the office worker and the soldier use competition as a way to advance and promote themselves. Competition, by fueling such advancement, draws members of groups together to beat whatever odds that they must beat. This perpetuates closeness. This is the test that we often fail because we, or our friend, misjudge what the other says. The term respectful sarcasm is the oxymoronic name that I use to describe this characteristic of good friendship.