I was using my Mac OS Sierra system the other day and came across this dialog box:
I'm sure Mac users out there have seen this dialog box countless times before as well.
I want to bring your attention in particular to the two buttons:
As you can see, there is an outline on the "Cancel" button (which generally represents focus), yet the "Shut Down" button is blue.
Intuitively, both type of "focuses" indicate that pressing the "Enter" key will trigger them; however, if you press the Space key on your keyboard, the "Cancel" option will be selected; however, if you press Enter, the "Shut Down" option will be selected.
Are there any usability principles that support this particular interaction? FWIW I found it quite confusing. I don't understand why Apple doesn't simply use one type of focus (i.e. either the outline or the blue color), instead of enabling both to appear within the same interface, generating confusion.