Sometimes that limit doesn’t exist. For instance, the infinite sum of +1 and –1 does not have a limit. The value of the partial sums flips back and forth between 1 and 0; it’s not really heading to a predictable destination. But with Achilles’ race, the partial sums go from 1 to 1.5 to 1.75 to 1.875 to 1.9375 and so forth; they get closer and closer to two. The sums have a destination—a limit.
