Me: For resting on one's laurels, and obscuring one's lack of recent progress, a focus on a cumulative number will work for a while. (Of course, if things are really bad, that will become noticeable as the curve approaches flatness.)
By the way, one thing I didn't particularly expect was Tufte's enthusiasm for the work of Richard Feynman, especially his famous Feynman diagrams. But in looking into that further, I find that I worked on a Michael Shermer column at Scientific American years ago (either fact checking it or copy editing it--can't remember) that involved Tufte, Feynman and the latter's diagram-illustrated van. As a further aside, I'm pleased to see that this TV movie is coming out: "The Challenger Disaster" (originally "Feynman and the Challenger").