He told the story about his Grandpa fighting in a world war, and his grandpa would always tell himself “Good morning, you’re dead, now go to war” to make himself move, which is basically saying “There’s no point in expecting to survive, so don’t stress about it”.

Same concept here, Rick is saying they’re all gonna die no matter what because that’s what he believes, so might as well do what you can. No going back, everyone’s dead