Personal injury lawsuits, such as those arising from automobile accidents, are most often based on a theory of negligence. In order to be successful in a negligence lawsuit, the plaintiff must prove each of the four elements of negligence by a preponderance of the evidence.
These elements are duty, breach of duty, damages, and causation. If the plaintiff fails to prove any of these elements, his or her case against the defendant will fail, and the plaintiff will recover nothing from that party.
Sometimes it is up to the jury to decide whether the plaintiff has met his or her burden of proof, but sometimes such matters are addressed during pre-trial proceedings before the judge of the court.