Well, there are many stages in a project and each of those stages needs to be well executed. There need to be decision points at the end of them.
There is usually a process which says that in the first instance what it is you're going to deliver, and roughly what you think the envelope is going to be. Then you do more precision in identifying what the system needs to do, and that gives you more precision in the budgeting. All through those points you need decision points that say either yes, you're going to continue, no, you're not going to continue, or you will continue, but there are some things you don't need to do. It has to be a very structured, very disciplined project management approach, also with proper governance and oversight, because sometimes the people responsible for delivery just want to deliver, and there has to be that other level, essentially, of due diligence in the project management from an oversight committee.