Effectiveness

"Unfortunately, I think that many RPG designers were and are flying entirely by the seat of their pants. Their attention was on in-game named elements like 'strength' and 'percent to hit' rather than Effectiveness. Such an approach to character design allows latitude for all sorts of emergent properties, such as point-mongering in Champions or the mini-maxing in most late 80s games, or any number of other 'take-over' elements of play that subvert the stated goal of the design." - Ron Edwards, "GNS and Other Matters of Role-playing Theory"

This makes me think of the simplicity and beauty of AW's stats (+2, +1, 0, -1) as pure measures of Effectiveness. You know precisely how those numbers will work and their relative strengths, even if it's your first time picking up the game.