From the following scenario, determine which one of the elements of negligence is unproven: A nurse is instructed to check a patient's vital signs every hour during her shift. During her shift, she gets involved with another task and forgets to check the patient for 2 hours. During that time, the patient has an allergic reaction to a medication that results in painful blisters on his legs. There was no indication in the medical records that the patient was allergic to this medication.