Question about Stimulus

Sure, let's try this sentence by sentence. The first sentence tells us that to understand some phenomenon, we need more than a few examples. This makes sense, we can't conclude that some social phenomenon is caused by something else only by looking at 2 instances. Essentially the author is saying we need a decent sample size. Next the author gives us an example, telling us that we can't be sure that an outcome is caused by some effect unless we can show that the effect doesn't occur without the cause, and that we know that the cause doesn't happen without the effect.