Iterations in mathematical modeling projects

In complex project environments, significant amount of rework is really common. The key is to identify the real source of rework that can be poor scope definition, planning issues, lack of high quality resources. However, when the scope is design and build a business simulation model, we can expect to have a iterative project definition and development. In this process, there is a lot of backs and forwards between contractors and owners, or between suppliers and contractors.

What do you think? Have you experienced this kind of projects?