It's expected to call if you can't make an appointment.
Jane was just in a minor car accident while driving to a business appointment.
Jane wants to address the accident.
After getting safely home Jane contacts the business to explain the situation.
Jane forgets about her appointment and spends the rest of the day talking to her car insurance company.
The business people show understanding for her situation and reschedule the appointment for the next day.
Since Jane missed out on her appointment without explanation her appointment is moved to the back of the waiting list.