You seem to have missed your mark and tried to load a page that does not (yet—or ever—or always—or sometimes—at least not today, we say) exist.
Then: what to do?
Hit the back button? Sure, that's fine.
Go to the main DIAGRAM entry page (it's the BEST)?
Or perhaps go to visit Wikipedia's AfD (articles for deletion) conversation page and argue for or rescue an orphaned article about to be deleted?
Or check out our editor's site?
There are many things to do. These are but a few of them.