I wholeheartedly agree with this statement.
While this doesn't pertain to civilian self-defense scenarios, the above statement is well illustrated when US Forces encounter certain "un-trained" elements and engage them in battle.
This is usually when the superior training, tactics, and mindset of the US soldier become evident.
The same could be true when a well trained civilian or off-duty LEO encounter an armed aggressor?
Not every aggressor will run or flee at the sight of a "waved" weapon, and when lead is snapping, training will greatly increase the likelihood of survival. (but most of you know that, as your training and skill far exceed mine)