Former Secretary of Defense Rumsfeld was criticized for commenting that you go to war with what you have instead of what you wish you had. He was not disparaging the military he was pointing out that there are always trade offs and imperfections in any system or institution. Protection versus mobility has been a trade off armies have always had to deal with and there is not perfect solution. We have seen this with armored Humvees that role over easier than the lighter version, body armor that restricts soldiers' movements and MRAPs that are too heavy to transport efficiently.
The latest issue is the debate over whether to add additional padding to the inside of combat helmets. Studies indicate it could reduce head traumas, but the extra weight would increase neck and shoulder injuries. The Army has decided to hold off for now on any modifications to the helmets. Although it is not a perfect situation, it is probably the right decision until new technology makes helmets stronger without making them heavier.