Scientific reasoning is defined by stories connecting 'what' to 'why,' but confirming a cause is challenging. The space between rigorous assessment of cause and reasonable speculation is riddled with consequential mistakes. In this unit, we highlight the most common mis-steps, learn to diagram and classify evidence from individual studies, evaluate a case for causality with diverse types of data, and triangulate to collect complementary evidence. Finally, we discuss the delicate art of communicating in a world that seeks 'whys' and weigh the importance of the explicit pursuit of cause in spite of its many challenges.