There must be something amounting to proof, either by direct evidence or rational inference of probabilities from established facts.'" Coyle v. Wrightson, 78 Mass. App. Ct. 1128 (2011) (quoting Bigwood v. Boston & N. St. Ry. Co., 209 Mass. 345, 348 (1911)); e.g., Williams v. Techtronic Indus. N. Am., Inc., No. 12 Civ. 11502, 2014 WL 2865874, at *6 (D. Mass. June 23, 2014) (summary judgment appropriate where plaintiff proffered insufficient causation evidence to proceed to trial), aff'd sub nom. Williams v. Techtronic Indus. of N. Am., Inc., 600 F. App'x 1 (1st Cir. 2015).
The plaintiff's burden of causation cannot be proven only through surmise or conjecture. Coyle v. Wrightson, 78 Mass.App.Ct. 1128 (2011). There must be either direct evidence or a rational inference of probability from the established facts which would allow a rational fact finder to rule for the plaintiff.