If your database of software projects has a thousand web browsers in it, you have to ask why all those programmers couldn't work together and write just ten or fifteen web browsers; maybe they're hobbyists who are reinventing the wheel for fun? If so, is that a good basis for estimating a new web browser?

The first time I worked on a database-backed web site, my team had written their own ORM, and while I was there we put together a thing so we could use the same view on more than one web page. The second time, we used web.py and no ORM. The third time, we used Ruby on Rails, which solved most of the problems we had on the first project I mentioned out of the box. Most recently, I used Django, which is roughly as convenient as Rails but easier to debug. I haven't tried it, but I'm guessing Claude Code could probably put together a usable Django site in a few minutes.

So achieving equivalent results requires very different activities over time, because each time someone does it, we accumulate not just knowledge but code that makes it easier the next time—thousands of times easier, if the novelty is small enough. This impedes estimation.

Often, too, the things we're trying to estimate are things like "add automatic Dart dependency support to Blaze". The time-consuming part of this is not breaking the rest of Blaze in the process. What reference class do we use for estimating adding new languages to Blaze without breaking it? Is Dart more like C++ or more like Go? These are questions for lawyers, not actuaries.

Maybe the videogames industry is different because they don't share code and don't maintain it? But it seems like an awful lot of games these days are getting written in Godot and Unity where 15 years ago people would have written their own engines... and problems that were major technical challenges for Quake are trivial now.

If someone wants ragdolls in their game, they can just license your code, right? They don't have to write it themselves. A dataset of how long it took people to implement ragdolls from scratch wouldn't provide any insight into how long it should take to integrate your ragdoll library.