There is factual evidence that, in general, the female brain deals with emotion and stress in a different way than the male brain. But that is a cut and dry approach, as many of both genders share "features" of the other sex's brain in various ratios, but far more common is a brain closer to that of the gender's norm.
Male brains are more focused on problem solving to deal with emotions and stress. Female brains are more apt to directly engage emotions and stress by focusing on the feeling, and taking it all in and using it. When women use those feelings, we men can find a LOT to dislike and fear. Just as women can absolutely hate when we get into our modes of management emotions and stress. Both are equally problematic, however, as one style of emotion management is complete aggression to push through the emotion/stress instead of other methods. Unchecked aggression based around some feelings can bring about a lot of problems in combat too. That's why individuals who have a brain that has some characteristics of both (regardless of which brain-type is more prominent in that person), are often far more capable in dealing with stressful time-critical tasks.
With that, women are largely in a lot of positions that requires seeing combat or having combat skills, but the Infantry and special units do not allow women to serve directly amongst their ranks. What research and reasoning these various services use to determine gender eligibility... who knows.