Couldn’t have said it better myself 
“…the iterative development process reflects what most of us actually experience as the reality of software development, that requirements cannot be frozen and new requirements are frequently discovered once programming is under way. Instead of trying to impose artificial deadlines and milestones on a project, as is common in traditional models of software development, the team can tailor the development process to conform to the situation as it actually exists, and therefore increase the chances for success.“
Can I have more details on this?