The process of gradual acclimation is one of the ways students are training to understand aggression, violence, and adversity. Because training in Viam Chao differs from, say, an elite course that requires weeding out candidates, it is important to gradually introduce some students to aggressive behavior.
This process can be used to acquire a tolerance for a wide variety of things.
The purpose of self-defense should be to prepare students for the realities of a violent attack. As such, it might seem as though "trial by fire" is the optimal way of dealing with this problem, but this runs the risk of forcing some students to quit who otherwise might have been able to achieve success over time.
The goal is to build up a student's confidence and tolerance over time. It is the psychological equivalent of progressive overload, which is when you build strength over time by progressively increasing the load. You wouldn't just throw a new person under a bar with 400 pounds on it and expect them to squat. Instead, you slowly inoculate the student to stress levels that lie just beyond their comfort zone. Once they are no longer uncomfortable by this, increase the intensity little by little until they achieve the highest levels of aggression.