I am continually amazed how well the concepts from martial arts, including tactics, training and teaching methods, etc., apply to other areas of life. Perhaps, with military training, the stakes are so high that the techniques evolved to crystallize the most fundamental and universally-applicable principles.
One of these principles is summarized in a maxim “Discipline equals freedom.” This might seem counter-intuitive at the first glance, but I find it is perfectly applicable to photography, where discipline comes up at several levels, from continuing practice and developing the shooting and post-processing skills to carefully and methodically packing the gear when going to a shoot to systematically experimenting with various camera and lighting settings during the shoot itself. The freedom then literally means creative freedom. When all the logistics and methodology is taken care of in a very disciplined inner, our full mental capacity, the entire bandwidth, is available for processing the incoming information, which allows us to react to changing conditions and opportunities during the shoot and to recognize potentially interesting patterns and combinations of lighting, composition, posing (in the case of portraits) and even future ways of using or displaying the images.
in other words, discipline allows us to reserve creativity for things that truly require it.