HOUSTON—There is a number guiding the basketball philosophy of the Houston Rockets. This number that informs every decision by the NBA’s wonkiest team and explains the marvelous season of James Harden is a very specific one: 1.16. That’s the number of points per possession they have to score to be the best offense in the history of basketball.

It’s such a powerful number that Rockets coach Mike D’Antoni, who has long been known for strategies that pushed the boundaries of his sport, realized he wasn’t pushing the boundaries...