They use their intuition, that is to say that they use their gut instinct. They follow what their insides (brain/heart) are telling them to do as opposed to seeking external ways to solve a problem or make a decision.
The military in particular teaches soldiers how to be more effective intuitive decison makers so that they are able to react more efficiently and effectively in the face of danger.
There are two things that a person or an animal is born with.They are intuition(the ability to learn something without tuition),insight(The act or outcome of grasping the inward or hidden nature of things or of perceiving in an intuitive manner.) For example, a child does not jump in the ditch(if it is not an accident) if he finds one while walking . At this time, in this particular case, his intuition works and forbids him from falling into the ditch.Similarly, all the dogs know how to swim;they do not sink except in some exceptional case.So, who taught them how to swim?Even in this case their intuition has worked.Now lets come to the insight.You might have felt it many times.For example , something comes ,all of a sudden, to your mind to warn you of the danger or to show the way out of the danger.This is actually insight.To sum up, the intuitive decision makers possibly base their decisions on the two things mentioned above.