Michael Herr said this quote

“ Well, good luck,’ the Vietnam verbal tic...It was as though people couldn’t stop themselves from saying it, even when they actually meant to express the opposite wish, like, ‘Die, motherfucker.’ Usually it was only an uninhabited passage of dead language, sometimes it came out five times in a sentence, like punctuation, often it was spoken flat side up to telegraph the belief that there wasn’t any way out; tough shit, sin loi, smack it, good luck. Sometimes, though, it was said with such feeling and tenderness that it could crack your mask, that much love where there was so much war. Me too, every day, compulsively, good luck: to friends in the press corps going out on operations, to grunts I’d meet at firebases and airstrips, to the wounded, the dead and all the Vietnamese I ever saw getting fucked over by us and each other, less often but most passionately to myself, and though I meant it every time I said it, it was meaningless. It was like telling someone going out in a storm not to get any on him, it was the same as saying, ‘Gee, I hope you don’t get killed or wounded or see anything that drives you insane.’ You could make all the ritual moves, carry your lucky piece, wear your magic jungle hat, kiss your thumb knuckle smooth as stones under running water, the Inscrutable Immutable was still out there, and you kept on or not at its pitiless discretion. All you could say that wasn’t fundamentally lame was something like, ‘He who bites it this day is safe from the next,’ and that was exactly what nobody wanted to hear. ”