I replied to Mzzry before I saw Joe's recent post. There is more than one recording on youtube of Phil Ochs singing When I'm Gone and you can hear that he does sing bracing and praise in the relevant lines in other recordings than the one Joe mentions. And those words make more sense. I suppose most of us don't sing Exactly the same words every time we sing a song. And some of us may make intentional changes: I sing "you won't hear me singing this song" instead of Ochs' "singing on this song" as the latter seems strange to me. And on some lines I sing "that's why I have to do it while I'm here" instead of "I guess I'll have to do it while I'm here." The main reason I do that is that I live in Ireland, and this way of using the word "guess" isn't a usual way of speaking here. Maybe "suppose I'll have to do it," would be clearer to listeners here. There is a different mood in the phrases using "guess" or "that's why"; the latter sounds more determined and the former betrays some reluctance. I can identify with the reluctance; sometimes we don't really feel like doing something but at the same time have a feeling that we really should do it.