So, yes, even bridges were built using the iterative process. It's just that the iterative process started long before you were born, and you found the world as it is without seeing the iterations that occurred before.
The same is true for doctors. There used to be all kinds of theories about how to cure the plague, or tuberculosis, or diseases we now know how to cure with a pill. Some of them worked, others didn't. Iteration at work, just over a longer timeline than your own lifetime.