I liked what he said about cardboard being more than cardboard. It reminded me of the following quote:

"Be deadly serious in your training. Your opponent must always be present in your mind, whether you sit or stand or walk or raise your arms. Should you in combat strike a karate blow, you must have no doubt whatsoever that the one blow decides everything. If you have made an error, you will be the one who falls. You must always be prepared for such an eventuality."

Gichin Funakoshi