Just like krp67 mentioned, I believe the most important part of a project is for it to be achievable. If the end goal of a project is not achievable, then working on the project itself is a waste of time. Other aspects of a project are not even relevant if the project is not achievable to begin with. For example, if a project is not achievable it is unlikely to be understandable. Along with that note, the affordability of a project, or its end result(s), would not be worth thinking about if a successful result is not feasible to begin with.