Back in the late 60's early 70's when I was Scuba diving 2 or 3 times a week, I also taught others how to dive after I got my instructor's license in '70. We would start out in a pool with just a mask, snorkel and fins until they were comfortable and in some cases, had built up enough strength and endurance to handle an hours worth of... swimming. Then we upped the gradient and went out in a calm lake, then the harbor and then the wide open ocean. Every step of this process has an added piece. As a person gains confidence with each step, they must also know what to do when something unexpected happens or their comfort level (stress threshold) is passed. This means practicing getting out of your gear, cutting off your weight belt, buddy breathing and a few other safety measures.
In handling a fearful, fear aggressive or aggressive dog, our goal is usually to get our dogs to be able to move toward or interact with their triggers, but they need to be prepared to respond to situations in which they are too stressed or over their skill level. Teaching the dog and the human to move away from triggers can be like cutting off your weight belt. Moving away is something that most fearful dogs want to do anyway. It’s easy for them and the human to learn and when super stressed, can be performed with little thought.