Why would a judge keep out evidence that seems true? Because evidence can be more misleading or emotionally damaging than helpful. Prejudicial effect means a risk that information will push a jury to decide a case based on anger, fear, sympathy, or bias instead of the actual facts. It does not mean the evidence hurts one side's case in the ordinary sense; most relevant evidence does that. The problem is unfair prejudice.

A lot of people get this wrong. Bad advice says, "If it's relevant, it comes in." Not necessarily. Under Rule 403 of the Arizona Rules of Evidence (2012), a court may exclude relevant evidence if its probative value is substantially outweighed by dangers such as unfair prejudice, confusing the issues, misleading the jury, or wasting time. Graphic injury photos, prior bad acts, or loaded language can trigger that fight.

In an injury claim, prejudicial effect can shape what the jury sees and hears. For example, after a crash involving a heat-related tire failure on an Arizona highway, a judge may allow photos that show vehicle damage but limit especially graphic images if they add emotion more than proof. The same issue can come up with heavy-truck collisions tied to mining traffic. These rulings affect settlement pressure, trial strategy, and how strongly causation, damages, and comparative fault are proven.