As we know waterfall is a linear sequential flow model.
We analyzed the requirements and freeze them and moved toward the designing phase followed by the Coding and testing phases for developing software named as DCA-I.
But the DCA-1 was not accepted by the client (doctor) because client was not satisfied, as the client want to change it in terms of graphics, functionality and features.
As, waterfall model does not allow changes after freezing the requirements so, it fails to deliver the software product.