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I find a few issues here, and I'm going to try and stay in my lane as much as possible because I know nothing about A&S other than what I saw on a documentary and what is discussed on this site.
-If you think that you'll walk away with no "what ifs" if you're not selected by the board, I think you're mistaken. It's just as easy to question your physical capacity as it is to question your mentality, attitude, etc during the Selection course. Everyone wonders if they trained properly before, during & after Selection. I bet a good number of those who are not selected also wonder the same thing about their attitude going into the course. I wasn't picked up for a LEO job when I still lived in PHX and I wondered constantly what I said/didn't say that kept me from continuing on in the process. Obviously two totally different jobs, but they are selection processes none the less.
-Regarding injuries. I got "hurt" (achilles tendonitis) and I decided I wanted to quit. That was my decision. People have pushed through worse pain than I experienced, I have no doubts about that. One guy who was at the school house had a broken foot because he kicked a jet ski trailer, it fell off the wooden block it was sitting on and crushed his foot. He's still there. He's LLD, but still hanging around. He didn't get dropped, he certainly didn't get medically separated from the Navy and he hasn't quit. Unless you have some near death experience, I don't really see all this being an issue. Again, I might be completely wrong because I know little to nothing about A&S and how they treat injuries. You also went from "plenty of Marines" to "one guy" in the same sentence.
-The fact that you included "bringing out my hate ape rage at another volunteer" gives me serious cause for concern. I think all SOF refer to themselves as Quiet Professionals for a reason. If you don't have enough self control to refrain from raging on another Marine during A&S you might want to seriously reconsider what you're getting yourself into.
These are just observations on my part, not shots at you by any means. I hope this helps some and makes you think.
Admin/Mods, if I'm way out of my lane, just let me know.