When making a budget, there is a process known as zero-based budgeting. In this process, instead of starting from the previous budget, you start from zero and work forward with the assumption that every item must be justified. This same procedure can and should be used when planning a project.
Starting from zero eliminates the problem 0f legacy processes and past projects that may weigh down a project. By starting from zero and justifying each part of a budget, process or project, you are getting a fresh perspective and are better able to adapt to new circumstances.
The drawback of a zero-based process is that everything must be created from scratch. You are not relying on past successes to propel you forward. It also requires that you redo work that may have already been done. While this does create more work, it allows you to plan with no assumptions and an ability to change direction if needed. The results can be well worth it.