When you get hurt, one possible cause could be negligence on the part of the person who injured you.
In that circumstance, a measure of the standard of care the defendant should have had is whether or not they were acting like a reasonable person.
The reasonable person is not an actual human being, but is instead a standard for actions. According to FindLaw, this legal term refers to the ideal of a person acting within the average standard of what others would do. This level of competence also encompasses failing to act if the situation calls for it. In that case, your actions may reflect negligence on your part.
This standard is subjective, which means it is not a specific set of written laws you can definitively use to determine who is at fault. Since each personal injury situation is different, this method relies on examining what the defendant knows and comparing it to how he or she should have acted in the same situation.
This standard means you should take precautions, such as avoiding dangerous activities while standing around vulnerable people. This can even include actions such as making sure to wear glasses while driving a car in order to prevent getting into car accidents.
Once facet of being a reasonable person includes acting on your full knowledge. This does not take into account facts you do not know, such as if you were to injure someone who you were unaware of. Common knowledge, which are facts that everyone in your community typically knows, does get taken into account. However, you usually have a duty of care to bystanders.