Non-Noticed
Riddle: You always use me every day. You never notice me every day. If you hit me it would do nothing. Without me the whole world would go upside down. What Am I?
Answer: Oxygen! You always use oxygen every minute and day. It's invisible. You would do nothing to oxygen except breathe it in. Everybody would die without it.
Source: https://www.riddles.com/8500
