To begin, negligence does not include those situations where a party has violated an existing law or statute. Those violations have an entirely different level of standing under the law, and in lawsuits.
Negligence is essentially judged on a “reasonableness” factor; that is, under these circumstances in which your injury occurred, how would a reasonable person be expected to act and respond? If the court finds that a reasonable person would have acted this way, and yet the party being sued acted in a substantially different way that helped cause the injury, then that party will likely be judged as being negligent.
Obviously, different people can have different opinions about how a reasonable person would act in a given set of circumstances. That is why we ask you for all documents relating to your case, and why we interview you multiple times. Depending on your case, we may also need to call upon expert witnesses and other parties to help the defendant, judge, and/or jury understand why a reasonable defendant would have acted differently.