This summary is not the rule. The rule text controls.
When a court makes a small mistake during a case, that mistake usually will not undo the whole case. This rule says that minor errors, like letting in a piece of evidence that maybe should not have come in, are not automatically enough to cancel a verdict, throw out a judgment, or force a new trial.
The main question is whether the mistake actually hurt someone's real rights in the case. If the error did not change the outcome or harm a party in any meaningful way, the court is supposed to ignore it and move on. Judges look at the case as a whole rather than getting stuck on small technical slip-ups.
This rule exists so that cases can be decided based on fairness and real justice, not on tiny technicalities. It keeps courts from wasting time and money redoing trials over mistakes that did not really matter. Only errors serious enough to affect a person's basic rights in the case can lead to a new trial or a change in the judgment.