This summary is not the rule. The rule text controls.
If a mistake happens during a trial, that alone does not mean the case has to start over or the outcome gets thrown out. Courts understand that small errors happen along the way, like a wrong ruling on a piece of evidence or a minor slip-up in procedure. These small mistakes are not enough to cancel a verdict or change a judgment unless they actually hurt someone's case in a real way.
The main question a court asks is whether the mistake affected a person's substantial rights. This means the error must have made a real difference in how the case turned out. If the mistake was minor and did not change the result, the court will simply ignore it and move forward.
This rule helps keep cases fair without letting every small slip-up cause a retrial or reversal. It pushes courts to focus on real fairness and real harm rather than picking apart every tiny error. In short, mistakes that do not truly hurt a party's rights will not undo a case, but mistakes that do cause real harm can still lead to a new trial or a change in the judgment.