While Johnny Cash famously walked the line, the defendants in Earnest v. Sanofi U.S. Servcs., Inc., did not successfully walk the line between Rule 701 and 702, with respect to a senior company employee in a products-liability case: “While parts of Dr. Kopreski’s testimony fall within the parameters of Rule 701, he also strayed beyond ‘facts, . . . subjective beliefs[,] and opinions,’ within either his personal knowledge or his capacity as Sanofi’s corporate designee. He testified regarding highly specialized and technical information related to Taxotere, the TAX316 study, and drug studies in general.” No. 20-30184 (Feb. 10, 2022) (citation omitted).