(Low Quality Comment Here) I, for one, have never had a tumble in KSP. Nope, every single launch, exactly as planned, all the way to orbit, and even the Mun. I have never once strapped a bazzilion first-stage engines in a row just to see what happens. Never once stacked them as high as I can. Nope - totally responsible game player over here.

Note: Trying to fly Jeb directly into the Sun was a real lesson in Angular Momentum.

I wonder if, after seeing that performance, they'll decide to weaken (or more accurately, remove extra weight from) structure they don't need.

My guess is that losing too many engines meant that they were too low, in too thick atmosphere for the speed they were reaching and with the reduced control authority form a missing gimbaling engine they couldn't maintain stability with those fins in the front. But we'll learn more later.

Is there a technical name for the "tumbling" phenomenon? When your first stage is almost out of fuel mass, so the CoG is not where it was when you launched and it's like you're pushing a bowling ball with a fishing pole instead of a giant steel beam, so you tip over.