The fact "You would add up numbers because the sum would be interesting or important to you." is illustrated with the story:1. Many things can be represented by numbers.2. For example, disk space is given in terms of total space and free space remaining.3. If I want to know how much space is left on my disks, I have to add up the amount of free space on each partition.4. The sum of these numbers tells me how long I can wait before I need to buy more disks.