In spite of what we all learned in our first statistics course, we just cannot resist attributing causality to correlation. We have to remind ourselves every time we see two events contiguously linked in time and space that the most natural explanation for their co-occurrence, namely, that one causes the other, might simply be false. The assumption of causality is one of the basic tenets of commonsense logic: Spring rains lead to flowers, knocking over the juice container results in spilled liquid, and clicking the power button on a small handheld instrument causes pictures to appear on the television screen. We all know, too, that it is counterexamples that compel caution in assuming the interpretation of causality: Superstition notwithstanding, carrying or not carrying an umbrella has no causal consequence for local meteorological conditions.