To prevail as the appealing party on an appeal, you must demonstrate that there is reversible error. Very generally, “reversible error” is an error which affects the outcome of a case and prejudices the losing party. State v. Buamruk, 280 S.W.3d 600, 614 (Mo. 2009). This can be a tall hill to climb. For instance, if an appellant is challenging the admissibility of evidence, the appellant must prove that particular evidence was outcome-determinative. In other words, the appellant must essentially show that the improper evidence directly led to the result and there was no other way of arriving at the conclusion. Courts have consistently reiterated this rule. Williams v. TSA, Inc., 281 S.W.3d 854, 872 (Mo. App. E.D. 2009) (“this court will reverse only if the prejudice resulting from the improper admission of evidence is outcome-determinative”).
Harmless error, in contrast, is not grounds for reversal. State v. Spica, 389 S.W.2d 35, 54 (Mo. 1965). A harmless error is, in short, any other trial court error that doesn’t prejudice a party or the outcome of the ultimate case.