Rule 45 Error without injury.

Here's a plain English summary of this rule:

An appeals court will not automatically throw out a verdict or order a new trial just because a mistake happened during the case. This applies to things like wrong jury instructions, mistakes about which evidence should have been let in or kept out, or errors in how the paperwork or procedures were handled.

Instead, the court looks at the whole case first. Only if the mistake likely caused real harm to someone's important rights will the court reverse the decision or grant a new trial. In other words, small mistakes that did not change the outcome are not enough to undo a case.

This rule exists so that cases are not overturned over minor slip-ups that did not actually hurt anyone's chances of a fair result. If you are appealing a case, you need to show more than just that an error happened. You have to show that the error probably made a real difference in the outcome.