The longer I work in this area, the more important I realize that a well defined business case is. This is also shown in global research. The most common reason that a project fail is not the execution, it is that it is not the right project with the right scope. The medicine is to take the business case process before the project start seriously.
It is though a complicated process. Good fragile projects has to survive. Bad projects must be killed preferably before they start.This is handled with the systematic business case process, but also by letting different projects with different risk and value take different segments of the project portfolio. I am deeply engaged in the business case educations