If you think of your inbox as a to-do list (where the most basic task is "read this"), then the most common pattern ITDBG (In The Days Before Gmail) for managing your to-do was using read/unread as your done/todo flags.
This was annoying; when reading an email that can't be actioned right away you'd have to go back and mark it as unread. Trivial, but it always felt like there was a better way.
When Gmail launched with it's Archive feature, it was definitely an "ah-hah!" moment. Now the read/unread flags had no hidden meaning, and your to-do list was simply whatever your saw in your inbox. When you action an email, away to the archive it goes.
Reaching inbox-zero is a gloriously satisfying moment. Why yes ... I WILL read some google news.