We know how to sum Arithmetic and Geometric series – Daichi's steady points or Hinata's multiplying impact. But many real-game situations aren't so simple. Imagine tracking Karasuno's score difference relative to their opponent during a set. Rally 1: Karasuno leads by 1 (u₁). Rally 2: Opponent ties, difference is 0 (u₂). Rally 3: Opponent leads by 1 (u₃). Rally 4: Karasuno ties, difference is 0 (u₄). The sequence of score differences might be complex. How do we find the total net change in the score difference after n rallies? The Method of Differences is a powerful tool for summing such series, especially when the general term uk can be expressed as a difference itself. It's like cancelling out the noise of the mid-rally chaos to see the final outcome!