What am I?

What force and strength cannot get through, I with my unique teeth can do. What am I?

I never was but always will be. No one ever saw me but everyone knows I exist. I give people the motivation to better themselves everyday. What am I?

As your ideas grow, I shrink. What am I?

Before I came, the world was darker, that's true. But beware, I can also kill you. What am I?

Riddles and Answers