I believe the word “literally” is used to distinguish between a figurative use of an expression and the literal use, i.e., taking the components of the expression to be what actually happened, not as purely idiomatic. If no distinction needed to be made, then the word “literally” could be and should be left out entirely (”I literally sat down in my chair!”). Therefore, in order to use the word “literally,” the phrase should closely mimic the original idiom, in both structure and usage.

The usage part is why I wouldn’t say “literally broke his heart,” because the figurative, emotional expression isn’t especially applicable here. To Ken R: had the lamp hit his face, I would prefer your “literally blew up in his face;” however, the author of the post only deemed my use unacceptable because of the word “plan,” not because of “backfire.” I thank him for OKing “literally backfire” more generally for this situation: A google of define:backfire yields a host of literal definitions, applying to torches, spray guns and normal guns, so I’d say any explosion in the opposite direction of where it was intended, towards the person who applied what was necessary for an explosion, is probably a loosely good literal use of “backfire.” Sloppy, perhaps, but not figurative.

So, in any case, I used the “plan backfired” phrasing, to mimic the structure of the figurative expression and then used “literally” to highlight the literal backfiring nature of the accident. Nitpicking “the plan backfired” versus “the implementation of the plan caused a backfire” may be officially correct, but I think the gist of the usage was fine.

Although perhaps I’m a poor commenter for this blog, as I’m not a “literally” snob at all. I don’t think people misuse “literally” by substituting it for “figuratively,” I just think they’re using it hyperbolically and thus slowly sapping it of its power.

-gar