Have you seen people drive? Road rage? Now think many of these same people with guns.
Target range practice is a very powerful biofeedback mechanism for teaching the suppression of the production of adrenaline and of all symptoms of excitement. Aligning gun sights - a pair of visual targets separated by about the length of the gun barrel (inches, a foot, or several feet), aligning them with a target (at tens of feet), and holding the alignment, gives visibility to even microscopic tremors and movement. Getting the image right and stable means drastically suppressing this movement. Over a number of range sessions, this leads to learning how to be icy calm, as a reflex, in the midst of a very stressful environment (full of intermittent explosions, bright lights, acrid smells, and odd-temperature winds).
(The effect is extreme. It was discovered that good target shooters, thinking they were just controlling their breath, had actually learned to "stop their heartbeat" - compressing the time between the pairs of beats before and after firing a shot and doubling the time between beats during the trigger pull.)
The result is that, after just a few good sessions, this becomes imprinted. Even in a rage, putting your hand on a gun drops you into that icy calm state.