Networks used to have a permitered-based security model.

Everything within the castle wall was trusted fully; everything outside it was fully untrusted.

The most important thing was to verify that the castle wall was strong.

But of course, all kinds of dangerous things can get through walls.

Toxic slime can seep through tiny cracks.

The modern architecture is zero-trust network architecture.

You assume that nothing is trusted.

"Never trust, always verify."

Every access request is authenticated and authorized regardless of source.

This allows fluid boundaries among everything.

By not trusting anything you can now get open-endedness.