When a premises is safe, people can enjoy visiting it without a fear of being injured. When it's not, it puts those same people at risk of serious injuries and can result in accidents. The owner of a premises should be reasonable and keep the premises maintained. Failing to do this can lead to legal problems for the owner in a case of a personal injury, since the person who was injured can claim that the owner was negligent and should be held responsible for any debts accrued because of said injuries.
What is a reasonable person defined as by law?
A reasonable person is defined as a typical person. When the law refers to the way a reasonable person would act, it's talking about how a normal, everyday person in the same situation would have reacted with all the same knowledge and information given to the defendant. If it differs from the way the defendant acted, then it could be shown that the defendant was negligent and unreasonable in the situation.
Here's an example. If your child attends school and there are dangerous stairs without handrails leading up to the school doors, a reasonable person in charge of the facility would take steps to eliminate those hazards and protect the children coming to school each day from falling down the stairs or tripping. If your child is hurt because the person fails to do this, then it would likely be able to be shown that the school was negligent and allowed an obvious hazard to remain on the property.
Source: FindLaw, "Standards of Care and the 'Reasonable Person'," accessed Nov. 10, 2016