Individuals have their own ritualistic tasks pre-determined by their profession. The skill of the doctor doing the hip replacement is only one component. This is not uncommon. The doctor who gave the injection is blamed. There are instances where an individual's competence or conduct is the main cause of a patient's suffering, and they should be held professionally accountable, but in most cases the cause is a combination of factors, not just the actions of one person.
Tribalism also determines how the system responds to an error.
While John will be told of the incorrect injection he will probably not be told the reason for the mistake for fear of litigation or complaint. If either occurs, the doctor will be blamed. The incident will be filed under medico-legal matters. Hospital lawyers will decide the response and lessons from the mishap will be lost. If patients were cared for by teams linked and working together it would minimise the errors because of improved communication, more appropriate decisions about the care, and focus on getting the best outcome.