What stops a human from being a fish?

This might seem like a confusing question, or an easy one.

There's lot's of differences, right?

One can breathe underwater, one has legs.

The world is a Tapestry, and while everything is woven together,

the threads are separate from each other.

But it is all still one connected thing.

What if there was someone who was able to pick out these boundaries?

Pull it out and do whatever he pleases with it?

At that point, what stops him from being a fish?

These would be Rebels.

They take the boundaries and twist them into their own rules.

They could even cut the separating thread if they wanted to.

But that would be Chaos.

Every human would be like a fish,

every fish would be like a human.

No, that should never happen.

Instead, these Rebels pull at the threads when necessary,

finding the loopholes in the Tapestry and slipping through them,

making themselves exceptions to the rules of the world.

They know what they can do,

and must make sure never to ruin the Tapestry.

After all,

when you can break the boundaries stopping a human from being a fish,

what stops a human from being the devil?