In my product development experience, I feel that customers can't wait until the completion of the entire project to get the final product. We assume that the software industry is pretty much similar to the manufacturing industry. As an example, a car manufacturing company produces the final product in a sequential, step-by-step manner. First they produce the chassis, then the engine followed by fitment, and so on.

To impress the customer, the traditional model assumes to deliver the big final product without the intermediate state. But in reality, the customer almost always tends to get a deviation of what they required. It is then too late to rectify it.

To resolve this challenge, the Agile model provides delivery to the customers frequently, in short iterations.