There is a difference between simple tasks and complex tasks. Simple tasks are tasks that we can perform sub-consciously. Complex tasks are tasks that require conscious thought and effort to perform to an acceptable standard.
Obviously there is also a difference between stressful and non-stressful environments/situations. Being injured, providing care for someone that is injured, experiencing sensory deprivation or sensory overload because of environmental factors (smoke, fog, bright lighs, darkness, loud alarms, etc.) can all contribute to make any situation become more stressful.
I always try to set myself up for success in any manner that I can control. I do this by trying to minimize the amount of complex tasks that I would have to perform under stressful circumstances.
For instance, let's look at a basic example. Is it more complex to drive a car forward or in reverse? Obviously, driving in reverse is a more complex task. Therefore, I prefer to back into parking spots when at all possible. Why? It's easy- when I arrive wherever I'm parking I am not in a stressful situation. However, I can't predict the future... So I don't know that when I leave that I will not be in a stressful situation at that time. Therefore I'd like to set up my route so that when I'm leaving I can drive my vehicle forward (a simpler task than reverse) so that I'm more likely to successfully perform that task if we are in a stressful situation when leaving.
Another example- I always setup and place my gear in the same manner/layout. Many times, after a day of training- I don't really feel like cleaning my equipment and putting it all back exactly the way that I usually have it. I fight that urge at all costs because at that moment I'm not in a stressful situation and therefore can go through and place the gear as needed. This means that later on, if I am in a stressful situation that I won't have to go through the complex task of locating needed gear or equipment because I will have already placed it in the proper locations.
Note that a complex task can become a simple task with enough training repetitions. For instance, reloading a handgun for a new shooter is generally a complex task. They have to think about the placement of their spare magazine, whether they use the slide release or power stroke method, etc. For a more advanced shooter, this task can be performed with virtually no conscious thought. It has become a simple task due to the number of repetitions that they have practiced on this task.
This means that a reload for a more seasoned shooter requires far less conscious thought to successfully perform than a less experienced shooter. This is the purpose of training. I want to constantly refine new skills so that I can shift them from my personal "complex" column to my "simple" column. Highly stressful environments or situations will deteriorate your skills and abilities rapidly. The more stress is added, the less proficient you will be. Therefore, always set yourself up for the greatest chance of success by training, repetition, gear selection and placement, and any other factors that you can control.
This doesn't only apply to "tactical" or "emergency" situations. During your work life, you can organize and prioritize tools and tasks in such a way that allow you to perform complex tasks while not under stress (deadlines, busy times at work, etc.) and leave the simple tasks to be done during high-stress. It's a great way to see how many of your day-to-day processes can be optimized for better efficiency. For me, this process has become addictive and I almost make it a game to see how I can apply it in various areas of life.
If it one day saves my life or the lives of others, great. If not, at least it makes my day-to-day tasks easy to perform.