The debate in the usability community about left vs. right for cancel and submit buttons is a long-standing one, and seems about as close to being resolved as the question of Ford vs. Chevy or Coke vs. Pepsi.

Of course, Cancel goes on the left, despite what Windows 3.1 would have you believe. Even more so on the web than in old desktop software, affirmative choices take you forward, and negative choices take you back. Just like reading a book, you look to your left when looking back. So when you’re clicking “cancel,” you’re really saying “take me back,” and that, naturally, goes on the left. Just because some chucklehead at Microsoft in the ’80s got it wrong doesn’t mean we should use such a silly convention purely out of bad habit.
But, since there are still people who engage in Wrong Thinking and expect Cancel to show up on the right, the one thing a designer should never do is put the Cancel and Submit buttons right next to each other. We’re spatial creatures, and prone to click before we read labels.
If you absolutely can’t get away with separating two such dangerously different buttons, at least provide for some kind of undo.
The folks over at Facebook not only went for the boneheaded backwards order of Cancel and Submit (or in this case, Send), but stuck the buttons incredibly close, and provided no way for the user to recover from the error.
The screenshot shows the message interface for Facebook on a desktop browser. Messages in Facebook are the equivalent of email for their users, and for some people, Facebook messages are replacing email. With such an important role to play, you’d think their designers would want to make sure Facebook messages at least reached the bar email set a couple decades ago. Instead, here’s a place that any user could compose a lengthy, thought-out message, and with one misplaced click, hit “Cancel” instead of “Send” and wipe out their entire work, gone, forever.
Put the Cancel button on the left where it belongs, get those buttons away from each other, and provide some way for users to recover their message if they happen to click the wrong button or leave the page / close the browser for any reason.