How does having one unsecured or obsolete device on a network make the entire network vulnerable?

Question

How does having one unsecured or obsolete device on a network make the entire network vulnerable?

In: 3

Answer 1

Pretend that you have an motel that has both inside and outside doors. You lock all the doors except just on outside door. If someone comes in that one door they can now get into the inside hallway and look around, break stuff and maybe find an unlocked inside door to another room because the room trusted everyone inside.

The unsecured device is that open outside door.