I was 15 when I first learned about this proof. The Mathematician, who was a volunteering math trainer to me, was the one who first introduced that proof to me.
He was talking about that beauty, how in math we can agree with someone “ Okay, let suppose that you are right” and then prove them wrong.
It’s amazing how powerful and beautiful the method of “proof by contradiction” is.
In addition, this proof became my favorite.