In the medical system today, there are specialists for every part of the human body. Cardiologists, pulmonologists, ophthalmologists, and the list goes on.
As a consequence, many people understand the body to be a group of separate mechanical parts, and with that mindset, the heart, lungs, and eyes are distinct and unrelated. This is akin to a car, as the odometer climbs, the brakes wear independent of the windscreen wiper blades, yet both components are critical to the safe operation of a vehicle on a rainy day.