As a former soldier - light infantry, or about as close to "special" you can get without actually getting the little badge - I'd opine that after a certain bit of selection, you can train everyone up to a sufficient level.
There isn't much to Army "training". Learn the specifics of weapons and kit, and then point and shoot, really. What separates a good soldier from a mediocre soldier is willpower. Good soldiers make the correct decisions more often because they can think clearly over pain, discomfort and stress - exactly what the article says.
SF training put a hyper-focus on this skill. So, to answer you question - pretty much all of it is innate. That has certainly been my experience. Some people are just better at this stuff than others, just like some people are better hockey players than others, even after years of training.
There isn't much to Army "training". Learn the specifics of weapons and kit, and then point and shoot, really. What separates a good soldier from a mediocre soldier is willpower. Good soldiers make the correct decisions more often because they can think clearly over pain, discomfort and stress - exactly what the article says.
SF training put a hyper-focus on this skill. So, to answer you question - pretty much all of it is innate. That has certainly been my experience. Some people are just better at this stuff than others, just like some people are better hockey players than others, even after years of training.