This is the truth.
A lot really depends on the situation and the strike itself. No two situations are exactly alike.
I've been kicked/kneed in the nuts now and then over the years, on purpose and by accident, with various results. Most often, I've fought through it. Oddly enough, the absolute worst ball shot I ever took was while playing tennis; I was running to my right to hit the ball underhanded when I completely miscalculated its position and missed it. Instead, it shot right into my nuts. That one put my @ss on the ground, and I couldn't get up for what seemed like a long time. Obviously, at that time, my fighting adrenalin was not active, as I was neither fighting nor sparring. But it hit so perfectly that I probably would've gone down anyway, though.