Well here I come with what I hope to be a serious answer... I think he is trying to say in order to prevent washing out, for example doing front flips. If you under rotate a front flip you will be back seat and prone to washing out, a softer ski will slip out more since it will flex and put you even further back seat, where as a stiffer ski will not flex as much, but this also has its negatives. The lack of flex in the ski holding you where you are when you are being forced backseat is the number one way (in my experience) to get shinbang, and also being backseat and not washing out has the potential to damage your knees, especially your ACL. Be careful if you under rotate, I normally will just wash out and not risk any damage than try to save a sketchy landing.
Cliffnotes: Stiff skis will help you ride away if you want to possibly break yourself, softer skis will flex more and be more likely to wash out.
You terrain park would be responsible for more deaths than Hitler. - 45.