(I found this in my notes--towards the bottom of the list--next to the note Can I, May I and Can I Go to the Bathroom.)
One of my personal favorites was being told that I would need something later in life. The teacher didn't know when or how, just that I would. Now that I am later in life I look back on these statement and realized they might as well have told me that at some point I would be shot by a mobster, they just don't know when or why.
The key thing this statement communicates to children is that the all knowing teacher knows that you will need some bit of information but that the children, in their limited knowledge and understanding will need to struggle and figure out, throughout life, how to use the information. If they happen to die before figuring it all out then they will die wondering "how was I supposed to use that incredibly valuable piece of information that no one knew how I would use it?".
What is tremendously better is what my college algebra teacher was explained to me: "higher math is required not because you'll actually need it, because you won't. Higher math teaches you to think differently, that's why we learn it." Thus explanation is so much better than "because you'll need it in some indefinite time in your life for some indefinite purpose."