Spoken like somebody that has never actually been in the gym.Not true. I boxed for six years, at the old Lincoln Heights Jail, in downtown LA, before it shut down, and was never knock down once, let alone "out."
There are many fighters who have never been knocked down, or out, in training. (The elite, of the elite, EVER.)
Being knocked-out, several times, in training, is basically confirmation of a lack of durability.