In the 1947 case of Callen v. Pennsylvania Railroad Co., the U.S. Supreme Court ruled in favor of the defendant, Pennsylvania Railroad Company, affirming a lower court's decision that it was not liable for injuries sustained by an employee who fell from one of its trains. The plaintiff, John Callen, argued that his fall resulted from negligence on part of his employer as they failed to provide safe working conditions under Federal Employers' Liability Act (FELA). However, the court held that there was insufficient evidence to prove negligence on behalf of Pennsylvania Railroad Company and stated FELA does not make railroads insurers against all accidents but only those caused by their own or their employees’ negligence. Therefore, without clear proof showing such negligence leading directly to injury or death cannot be assumed merely because an accident occurred.

In the dissenting opinion for Callen v. Pennsylvania Railroad Co., Justice Robert H. Jackson disagreed with the majority's decision to overturn a jury verdict in favor of an injured railroad worker under the Federal Employers' Liability Act (FELA). He argued that this was not a case where there was no evidence at all, but rather one where different conclusions could be drawn from it. In his view, weighing and interpreting evidence is exclusively within the province of juries, not appellate courts. The judge believed that by substitifying its judgment for that of a jury on factual matters, even when those facts are disputed or doubtful, would undermine FELA’s purpose: to shift part of human risk inherent in railroading from workers to their employers who can reduce accidents through better safety measures and distribute costs through rate adjustments or insurance.