In fact there's is no single piece of evidence that would corroborate the idea that being better (i.e. trying to achieve perfection) is more expensive than, not trying to achieve it.
But let's get back to the examples that I just ran into on the net:
The first fallacy: the cost of Zero-Defects
In a post by psabilla in shmula we are faced with the idea that Zero Defects would be too expensive to achieve therefore, the author suggests, it should not even be tried.
In here the author even presents a graph of the theoretical cost of achieving Zero Defects. It worthwhile to notice that this graph is a completely hypothetical graph, no connection with actual real data collected from a real project trying to really achieve Zero Defects.
Further along the author unmasks the prejudice that does not allow a more clear view into why Zero Defects are not only possible, but if achieved will yield a much faster _AND_ cheaper process for software development.
The author writes:
As defects are identified and eliminated, there will be theoretically few defects. But, this means that identifying defects will require more effort and will become more and more difficult, thus increasing the costs of this activity, along with the subsequent costs to fix the defects identified: The costs to inspect and test increases as there are fewer and fewer defects.
In the paragraph above take note of the causality that unmasks the prejudice. The author starts by using a seemingly obvious phrase (removing defects leads to less defects being present) and then exposes the prejudice behind the article: less defects means that it will be more expensive to identify other defects.
Think about that phrase for a minute: "if we have less defects it will be more expensive to find other defects".
Here are the problems with that phrase
- It assumes that the role of testing is to find+remove defects: This is wrong, very wrong, because if a defect is added to the code base and only found much later that is indeed a much more expensive process than if we remove the defect closer to the source. Ideally immediately after it has been added to the source. I've written about this here. In other words: the role of testing is to prevent defects from being added to the source in the first place!
- The second (wrong) assumption is that if we have less (presumably a lot less) defects we are then going to spend more money on finding the few that are left. Well, I don't know what projects the author has worked on, but as of today I don't know of any software project that would have achieved zero defects upon release. This actually means that at some point in the software development+release process the project team will say "alright, we have spent enough time looking for defects and not finding them, it is time to release". This suggests that project teams are smart enough to know when the cost of searching for a defect is higher than the benefit it brings.
Assuming the arguments above are sound we have to acknowledge that the basis for the argument by the author is false and indeed Zero Defects is not only possible, but also (given people's pragmatism) does not represent any additional cost to projects.
The second fallacy: You can't get rid of defects without Inspections
Jurgen Appelo, uses some of the data/arguments from the previously cited post to go on to say that Zero Inspections is an impossible and too costly goal. Note that Jurgen's post touches on other issues, I will not comment on those and restrict myself to the issue surrounding the impossibility or prohibitve cost of Zero Inspections.
The author builds on the (already demonstrated wrong) argument that Zero Defects is too expensive to also say that we cannot live without Inspections.
The author confuses Inspections with normal ways to prevent errors from going to far. I would agree that we need to have some inspections, but not in the way that Jurgen, or indeed Tom Gilb have suggested.
There's some data already available (albeit disputed) that Inspections provide little or no value and mostly focus on inspecting the format of the artifact (templates, coding conventions, grammatical defects, wrong color, wrong use of terms, etc.) and technicalities (curly braces where none are needed, too short method name, etc.) instead of the fundamental Defect magnets that logical flaws of thread-safety represent. This is also my experience.
Taking the example of code reviews, these are often more useful for knowledge sharing than for defect identification (not to mention that it is quite expensive to review code -- although you should do it in many situations :).
My point is this: Inspections have been around for 10's of years, why is the software industry consistently ignoring them: because they don't deliver enough value! At least Inspections in the sense of "let's get together in an additional meeting and review this artifact to make sure it has good quality, and then follow that with a formal process to change/update the artifact and get it approved" (code can be the artifact).
Ad-hoc inspections are often much more convenient, cheaper and value-adding but this is not what Jurgen or Tom Gilb suggest should be done! Hence my problem with Jurgen's article.
Zero Inspections is not only possible (been there done that, even with large - big L - projects) but it is also a catalyst for the teams to prepare not to need those Inspections. Imagine this: if you have an Inspection coming up for that last module you changed how motivated are you going to be do your job in the best way possible and aim for Zero Defects? The answer is: not motivated! In fact, my experience is that people will just aim to "avoid being embarrassed/humiliated during the Inspection meeting".
If you have the practices that support it and aim for Zero Defects (automated test, early Acceptance Test definition, etc.) you are going to be much more motivated (and supported) to achieve a very low (approaching Zero) defect count!
Oh, and by the way it follows that if you can achieve (proven) Zero Defects why do you need the Inspections?
There's a hidden (ok, not too much) argument here. If you aim for (and approximate) Zero Defects then your process will be faster (less rework due to defects, less inspections) and cheaper (less technical support needed, less reimbursements to annoyed customers).
But there's a catch! The catch is: you cannot achieve Zero Defects or Zero Inspections unless you invest in and change the way you work! It takes effort, dedication and constant experimenting and learning. However, if you don't do it your competitors will. Sooner or later. And when they do you will find yourself with a more expensive product that annoys your customers. What do you do then?