Why a knife can cut anything but our finger can't?

Hi guys ... how you all?  Today I share with you a new thing...

Do u think anytime that why a keen knife cut anything but our finger don't cut that?
Let's explain the answer.

By the physics formula,  we know that,
               

Why we see a object bigger or smaller?

Hi. Now I share you a simple knowledge of seeing ....
Do we know,  why we see a thing bigger or smaller?
Don't??  Let's know that...

We see a thing bigger or smaller for focus angle in our eyes.

Let me explain.