Russia has a lot of recent experience. Experience does matter at first, because until a person experiences true combat, you cannot know how they will react. But the people who will cower or freeze in actual combat get winnowed out pretty quickly or learn to deal with it and fight. Obviously, on the planning and strategy side, experience is important just as it is with anything. You learn from your mistakes and from what has worked before.
But in the trenches, dealing with the actual soldier, the first time in combat is apparently a very difficult thing to predict. All you can do is train the soldiers so that they don't have time to think, don't need to think, in fact do not think because thinking leads to recognition of bad odds and likelihood of maiming and death, a sure road to paralysis. This has been shown repeatedly through history. The new guys tend to die at a much higher rate than the experienced ones.