Here is another thought related to the issue of safety and planning. Some have argued that the ability to plan a safe dive is the key component of the definition of a safe diver.
Before his last dive, David Shaw and a highly experienced tech instructor put together a huge team with the best equipment they could get. They had news coverage on site, and they had a chamber on site. They talked through every aspect of the dive over and over again. All divers on the team (I think there were 16) had specific jobs and knew to the minute when they were supposed to enter the water to do their parts. Shaw himself rehearsed every step of his role to make sure he could do everything within the very short bottom time he would have at 270 meters of depth. He had been to that depth before and knew his equipment could function there. (No one else could say that.) He was confident.
Two mistakes were made. One of them was very understandable and ultimately not serious, but the second was shocking and fatal. They were recovering a body they expected to be skeletal and negatively buoyant, but it had turned to soap within the wetsuit and floated, making the planned recovery process impossible. After the dive, experts explained the biological process, leading the surviving dive leader to ask where all that knowledge was before the dive. Still, once Shaw realized the problem, it was not fatal because he aborted the attempt at the appropriate pre-planned time limit.
That was where the second error came to play. During planning, they realized that the helmet camera he was wearing prevented him from doing what he normally did with his dive light when he needed to work with two hands: loop the cord over his neck. In the planning sessions, he decided that he would just let it dangle. When I read that, I almost shouted "What the H--- are you thinking?" His dive instructor friend (who got severe DCS on the dive when he tried to save Shaw) later said he never heard that part of the plan, or he would have nixed it. If I had announced that idea during my intro to Tech class, I think my instructor would have hit me. There has to be something about his gear setup that I don't understand, because to me there is such an obvious clip-off solution--the one I would have used without giving it a thought--that I cannot believe it was not used. As any cave instructor would predict, when Shaw aborted the dive and turned back to the ascent line, he found that his light head was thoroughly wrapped in the line leading to the body, and with his CO2 levels raised to an extreme, he was unable to free himself in time and passed out.
So how does someone as skilled as that make such a basic mistake and even include the mistake in planning, without any of the other highly skilled divers there pointing it out? Is a diver who makes such a basic mistake a beginning or an advanced diver? If that means he is not an advanced diver, then I would argue that there is no such thing.