First thing that comes to mind isn't Vonnegut's philosophy, honestly—it's just how weirdly comforting I've found that phrase on bad days. It slips out sometimes when I see another grim headline or when something minor goes wrong, like missing a train. It's not a shrug of indifference, more like... acknowledging the chaos exists and you're still here. The repetition in 'Slaughterhouse-Five' makes it a weird mantra. After a while, it stops being just about death and becomes about everything absurd you can't control.
Some folks say it's nihilistic, but I disagree. Nihilism feels empty. 'So it goes' feels like a deep breath. It's the verbal equivalent of Billy Pilgrim becoming unstuck in time—you see the awful thing, you note it, and your consciousness just... moves along. It's how you survive a bombing or a Tuesday. Vonnegut gave us a tool for grief that's dry as a bone and strangely kind.