There are two variations of the Rule of Three. The first, from Secrets of Consulting: A Guide to Giving and Getting Advice Successfully by Jerry Weinberg is about evaluating options:
If you can't think of three things that might go wrong with your plans, then there's something wrong with your thinking.This sounds rather negative, but if you think for a second, it makes sense, and it's really about being constructive. Design decisions are about evaluating trade-offs. You want to pick the decision that has the problems that you can live with. When we've been struggling with a problem and come up with a plausible option, we tend to want it to work. If you don't think about what might go wrong you're making it harder for a good idea to succeed. The worst that can happen is that you find that your "great" idea doesn't solve a likely problem. This is good. The best is that you discover that your idea addresses issues you didn't consider. This is very good.
Is thinking up three possible problems with a decision foolproof? No. But this approach strikes a good balance between Big Design Up Front and being too impulsive.
Weinberg's original Rule of Three is great when you have an option to evaluate, but how do you develop options? In Behind Closed Doors: Secrets of Great Management (Pragmatic Programmers), Johanna Rothman and Esther Derby describe a related Rule of Three: Always come up with (at least) three alternatives when trying to solve a problem. While 3 can be an aribitrary number, Johanna and Esther explain that:
- One alternative is a trap.
- Two alternatives is a dilemma.
- Three provides a real choice (and gets people in a frame of mind to come up with more).
You may not always need three choices when looking at a situation. And when you have a solution in mind, you may not always need to think of three things that can go wrong with it. On the other hand, the cost of following this process is small, and the benefits are great. Make the Rules of Three a habit and you may find yourself making better decisions.