I have written and spoken many times about the importance of getting started. This is a key idea in agile software development (or for that matter, to many other kinds of work). If you refuse to start projects until you fully understand how they can be completed, you will miss many valuable opportunities.
When in doubt, start. But start with a modest budget, because there is an opposite and equally unavoidable fact of life. To complete a project of any size (one person-hour, or 1000 person-years), a sufficient effort must be mustered. Sometimes some of my fellow agile lists talk about working on a huge project one bite at a time, planning just the next few iterations, just the next scrum, whatever. This is all good, this is all agile. But it is important not to ignore the size of the thing you’re trying to accomplish.
To accomplish something of size (fast enough for it to be valuable) requires an approximate overall understanding of its size, then committing sufficient “resources” of all kinds:
- Project managers
- Physical facilities
- The list goes on
If it is not possible to commit enough firepower to the job at hand, then the right time to cancel or rescope an effort is at the beginning, not halfway through (the infamous point at which you are 90% of the way done but have 90% of the work still remaining). Keep that in mind next time a project is proposed. Understand the resources that can be committed, the overall scope of the project, and if they don’t fit, pick a different project.