Ambient here is defined as the programmer assumes that they don't have to ask permission, nor does the runtime, you can just open any file at will that the user

Ambient here is defined as the programmer assumes that they don't have to ask permission, nor does the runtime, you can just open any file at will that the user is allowed to access, without restrictions. So if an image viewer is given permissions to access your photos, it includes a broad swath of permissions, including the ability to just corrupt them all. With a capabilities based system, the image viewer would get access to a single photo, or a folder of them, and perhaps read-only access, decided by the user at run time, instead of the system administrator at some earlier time, or the manufacturer as a category choice.