Where the court used a confusing and misleading analogy to amplify the jury instruction defining “reasonable doubt,” the error was not harmless and required reversal. The trial court here explained the concept of reasonable doubt with analogies regarding vacations and car accidents, prompting the appellate court to observe that “[w]e can all describe situations where people make serious decisions in spite of grave reservations about the outcome … Such situations cannot be equated to the level of conviction necessary for finding guilt in a criminal case.” Because the erroneous instruction affected the defendant’s substantial rights, the error required reversal in spite of defendant’s failure to object.