found this:

Keith Urban talked to The Boot about the re-recording of his song, 'Got It Right This Time,' which was inspired by his marriage.

It's interesting, because the song's hook is, "I think I got it right this time." And I'm certainly at a point now where there's no thinking involved! [laughs] There's a little more conviction than that. And I had that full conviction when I wrote it, but as a songwriter, there are choices made with words because they sing well. So, "I know I got it right this time" just doesn't sing as well as "I think I got it right this time." But as the song has evolved and grown, our marriage has evolved a lot. So [on the new recording], at the very end there's an ad-libbed line that says, "I mean, I know I do." [laughs] Songs are interesting, because they're written at a certain time in a writer's life and they mean a certain thing, but often, the really magical ones develop deeper meaning. And this song has definitely grown to have a deeper meaning for me.

http://www.theboot.com/2008/07/09/story-behind-the-song-got-it-right-thi...