Answer:
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
I tell people to be careful when handling boxes.
A spirited jig I dance bright, banishing all but darkest night. Air can't kill me but water can. Share me, I won't get less unless wind ruins me. What am I?
I am a precious stone, as clear as a diamond. Though you can walk on water with my power, try to keep me, and I'll vanish in an hour. What am I?
One simple click, one simple flash. A piece of memory, for years I'll last. What am I?
I am your mother's brother's only brother in law. Who am I?