Do I need an expert for that?

While arising in the specific context of a defective design claim under state law, Stewart v. Capital Safety USA addressed a broader question about when expert testimony is required to prove a point, as opposed to observations by knowledgeable lay witnesses. The Court held: “To find injury causation here, a jury would at least have to conclude that a different lifeline cable or a different warning would have, under the circumstances of this accident, prevented Stewart’s death. Thus, a jury would be confronted with questions that require a degree of familiarity with such subjects as physics, engineering, and oil rig practices and procedures. This case therefore raises questions that are of ‘sufficient complexity to be beyond the expertise of the average judge and juror’ and that ‘common sense’ does not ‘make[] obvious.'” No. 16-30993-CV (May 30, 2017; published Aug. 21, 2017).