There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it. If you are not allowed to move in any way (other than your eyes).
Where can you place an apple so that all but one person can see it?
It is a protector.
It sits on a bridge.
One individual can see directly through it , while others wonder what it hides.
What am I talking about ?
On 20 planes I may be, but only rest on one you see. I can help you or hurt you, depending on where I lay. Because I am not the kind you use everyday.
What am I?