This is exactly what I've said. My initial "proof by example" was an answer for the op's statement:
> Proof by example or analogy is not a proof.
So as you also said "Of course you can prove something exists by an example".
To answer this:
> Proove that you can't walk. Don't walk.
As I said, proof by example works only
> to prove that something exists or that a property is not valid for every element of a set.
Divide your lifetime in seconds. With that, you're trying to proove with the property "walk" isn't valid for every element of the set lifetime. To proove that the property can't walk dosen't hold for every element of the set, just show an example of second while you were walking and you're done.
> Proof by example or analogy is not a proof.
So as you also said "Of course you can prove something exists by an example".
To answer this: > Proove that you can't walk. Don't walk.
As I said, proof by example works only
> to prove that something exists or that a property is not valid for every element of a set.
Divide your lifetime in seconds. With that, you're trying to proove with the property "walk" isn't valid for every element of the set lifetime. To proove that the property can't walk dosen't hold for every element of the set, just show an example of second while you were walking and you're done.