Rule Of Threes: Really?

Is the "Rule of Threes" (3 shots at 3 yards in 3 seconds or less) what happens most of the time in a life or death citizen self defense encounter? Where did that statistic come from? Is that what you should expect if you ever need to defend yourself? And, how do single action revolvers compare to semi-autos if it's true that 5-6 shots is enough and no reload is needed?

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