“There’s another familiar lesson in this graph: output metrics—the data we graphed above—are far poorer indicators of trend causes than input metrics. It turned out in this case that the cause of our decelerating growth was a reduction in the rate of acquiring new customers—but nothing in these graphs gives any clue to that cause. With a sizable existing business, if you only pay attention to the output metric “revenue,” you typically won’t see the effects of new customer deceleration for quite some time. However, if you look at input metrics instead—things like “new customers,” “new customer revenue,” and “existing customer revenue”—you will detect the signal much earlier, and with a much clearer call to action.”