Sometimes proving negligence is straightforward. Suppose that Cis-neros goes to the neighborhood garage to have the wheels of his Maserati balanced. After driving away, the right front wheel falls off. Cisneros gets out and looks around, but is only able to find three of the lug nuts that hold the wheel on. He returns to the station, where another customer tells him that he saw the mechanic leave the other lug nuts off. Negligence? No problem: What happened is clear from direct evidence, the testimony of the other customer, and a jury would almost certainly conclude that the mechanic was negligent in failing to replace all the lug nuts.
Would that all negligence cases were so easy. If they were, few negligence cases would be tried, because cases in which liability is clear almost always settle before trial. The cases that reach the trial stage are likely to present substantial disputes of fact, in which proof of essential elements-particularly negligence-is more problematic.