Re: Injury and Responsibility
In all realms of activity, fatigue is a common cause of injury. Swollen joints are much more susceptible to injury. Fatigue creates concentration problems which can cause folks to lose their "presence of mind" and lose their form which often leads to injury whether self-inflicted or visited on a fellow.
But... It is hard to tell if you have successfully hammered a reflex unless you've tested it under the duress of fatigue. If you can execute flawlessly while completely knackered, then you know you can do it without thinking - it has become a reflex.
Furthermore, as Dirty Harry famously said, "A man's got to know his limitations." And yet, unless you've been driven to your physical and mental limits, you usually won't actually know what they are. Unfortunately, the process of discovering your limitations can be dangerous which is why everyone in a dojo needs to be safety conscious. "Players" in every sport need to be yanked from the "game" if they cannot hold their form - they have become a danger to themselves and others.
Some folks actually know their limitations because they have been in extremis. But the process of being in extremis can be life-changing in not necessarily a positive way. So I think it is important to test one's limits slowly, safely and carefully. And understand the risks.
Don't take this as a "don't try, don't push." Most people are capable of things they never imagined - but don't let your imagination get ahead of prudence and skill.