The planning phase is very important because it will set the foundation of how you’re going to tackle this project. If poorly planned out then the project could face delays, cancellation, or might not be profitable in the end for the company because the development process was poorly executed. A well planned out project can have impacts minimized by unforeseen circumstances. I also agree that going back to an earlier phase doesn’t necessary mean a bad thing, depending on the impact to the project. During each phase there should be some leeway factored in, just in case of situations like this where an unexpected problem came up. There may be times where you go back based on new feedback your receiving or team members have found a better optimized method that could be beneficial to the project.