Correlation Is Not Causation

Two things being correlated means they move together statistically, but that pattern alone does not tell you that one causes the other. The relationship could run the other way, both could be driven by a third hidden cause, or it could be pure coincidence.

This is the single most important warning in data analysis. Ice-cream sales and drowning deaths rise together, but ice cream does not cause drowning — hot weather drives both. Whenever someone reports that A and B are linked, ask whether a confounder, reverse causation, or chance could explain it before believing A causes B.