A vehicle driven by the testator of Channell (defendant) collided with a vehicle driven by Albert Sampson (plaintiff) in Maine. Sampson was seriously injured and filed a negligence suit in federal district court in Massachusetts against Channell. Channell argued that Albert was contributorily negligent in causing the accident. Albert requested that the district court instruct the jury on Massachusetts law, which required Channell to prove Albert’s contributory negligence. The district court declined and instead instructed the jury on Maine law, which provided that the burden of proof regarding contributory negligence was on Albert to affirmatively show that his actions did not contribute to cause his injuries. The jury held for Channell on the issue of contributory negligence, and the court entered judgment in Channell’s favor. Albert appealed, arguing that Massachusetts law determined the burden of proof.