The level of the involvement or presence of an entity or person at a location where a serious injury has occurred relates to the issue of "notice." Notice is a legal concept which says that a party will not be liable or found negligent for an injury unless they "knew or should have known" of the defective or dangerous condition that caused the injury. Alternatively, a party might be found negligent if they created the defective or dangerous condition that led to the accident or injury; however, in this case, the issue of notice is not relevant because liability derives from the affirmative negligence of the tortfeasor or negligent party. An owner will often give the excuse that they were out of possession and never present, claiming that they gave full possession to a tenant, so that they can claim that they did not know nor could they have known about the defective or dangerous condition that caused injury. Showing that the responsible entity actually was aware of the dangerous condition can be crucial in a personal injury or death case. This is known as "actual notice" and demonstrating it goes a long way toward proving liability. Absent actual notice, what is known as "constructive notice" may also be sufficient to prove liability. Constructive notice is most often proven by presenting evidence that the dangerous condition was present for a prolonged period of time, or at least for a long enough time that, in the exercise of reasonable care, the responsible party knew or should have known of the condition and thus done something to correct it. Proving that a responsible party had actual or constructive notice often involves obtaining the testimony of eyewitnesses who have knowledge, through their observations, of conditions that existed. These observations could involve transient conditions such as the presence of snow or ice, or the presence of a slippery substance, such as on a stairwell or in the aisle of a grocery store. If the witness can attest to the presence of the dangerous condition for a period of time within which it should have been cured, then liability may attach to the responsible party. In some cases, the nature of the condition itself may be evidence of how long it was present (such as the buildup of a large amount of dirt or debris). On the other hand, if for example one slips on water on a stairwell, with no evidence of how long the water or liquid was present, than proving notice may be impossible. For instance, another tenant spilled some water moments earlier, without presenting the landlord with the opportunity, even in the exercise of reasonable care, to clean the dangerous condition. The aforementioned example of constructive notice highlights the fact that having an accident and sustaining an injury does not automatically entitle one to compensation. Proof of negligence, which is the failure to exercise reasonable care, is essential to obtaining compensation in a lawsuit. The law in New York State places the burden of proof upon the plaintiff (the injured party) to prove that it is more likely than not that the defendant was negligent. Another more technical way to describe this burden of proof is to say that the plaintiff must prove his or her case based on a preponderance of the evidence in favor of the plaintiff. If from the evidence there is no inference or preponderance one way or another, the plaintiff has not met his or her burden. Proving liability in a civil personal injury case involves, at a minimum, tipping the scales ever so slightly in favor of the proof set forth by the plaintiff. Proving notice is crucial to meeting this burden of proof in any type of premises liability accident.