The U.S. Supreme Court case Robert O'Neal v. Fred McAninch, Warden (1994) revolved around the issue of habeas corpus relief in relation to a state court conviction. The petitioner, Robert O'Neal, was convicted for murder and attempted robbery in an Illinois state court. He appealed his conviction on the grounds that he had received ineffective assistance from his counsel during trial because they failed to object to certain jury instructions which were allegedly erroneous and prejudicial against him. The District Court denied O’Neal’s petition but the Seventh Circuit reversed this decision stating that there was reasonable probability that without these errors by defense counsel, outcome of proceeding would have been different. However, when it reached the Supreme Court level, justices held a 5-4 majority opinion written by Justice Stephen Breyer who stated that if judges are in "grave doubt" about whether an error has affected verdict's outcome then such uncertainty should be resolved in favor of defendant seeking habeas corpus relief i.e., prisoner should get benefit of doubt. This ruling set precedent for future cases involving similar issues related with habeas corpus petitions where impact or harm caused due to alleged error is uncertain or unclear.

In the dissenting opinion for Robert O'Neal v. Fred McAninch, Justice Scalia disagreed with the majority's decision to remand the case back to lower courts based on a "grave doubt" about whether an error was harmless or not. He argued that this approach is inconsistent with previous Supreme Court rulings and federal law, which require defendants to prove that an error had a substantial influence on their trial's outcome. Instead of adopting this new standard of "grave doubt," he suggested sticking with existing precedents requiring clear proof of harm from any errors made during trials. Furthermore, he expressed concern that this ruling could lead to more appeals and retrials by encouraging defendants who cannot definitively prove they were harmed by an error but can raise serious doubts about its impact.