What is ecological fallacy?

What seems contradictory is often two statements true in different contexts.

Example: A doctor says 'exercise reduces heart disease risk.' A cardiologist says 'exercise increases risk of cardiac events.' Both are right — the first is talking about habitual moderate exercise over years, the second about vigorous exertion during a single session in someone with existing heart disease. The contradiction dissolves the moment you ask: exercise for whom, what kind, over what timeframe?

This concept is part of Contradiction Resolution in the How to Think curriculum, which builds the epistemic infrastructure for contradiction resolution.