I don't think that it is possible to completely eliminate "stress" or "jitters", but it is possible to learn to "power thru". When I was in the military, we did some very complex missions that required multiple skill sets to complete. We were able to do this by training- lots of realistic training, as a team. Much of this training was done under man-made stress. We also trained in all terrain, weather, and light conditions. In order to induce physical stress reactions in training, we incorporated physical activities like pushups, wind sprints, and rope climbs just prior to an exercise, to increase heartbeat, breathing, and other effects. My personal results- yes, there was some jitters heading out to a mission, dry mouth, etc., esp. during that air or ground movement to the target. Just prior to things "getting real", my heart felt like it was going to fly out of my chest. But once the breaching charge or first flash bang went off before we went in, or the enemy fired that first RPG to start their ambush, things slowed down, focus improved, and the team always did well. The key is lots of training and developed talent. This is the same thing that separates the enthusiastic youngsters playing football in the backyard from pros in the NFL. Training is sacred. I still try to maintain a consistent training regimen: PT in the AM for 1 hour 3x a week, 3 sessions of MMA a week in the evenings (with guys in their 20's- I'm 53), and 2 live fire sessions per month (down from 1 a week due to issues with ammunition resupply). I'm convinced that maintaining skills pays off in terms of health in general and survivability in particular, should the need arise. I'm also convinced that when I caught the covid in July (yes, I am a Fl statistic), this played a role in the fact that I had minimal symptoms and only felt bad for 2 days.