This post is interesting at three levels. It is a meticulous case study of why contact tracing, and particularly pseudonymous contact tracing, and particularly app-based pseudonymous contact tracing is a hard problem (maybe even a wicked problem). It is an example of a more general phenomenon that describing a policy aspiration generally turns out to be much easier than describing, let alone implementing, a way of meeting that aspiration. And it illustrates the adage (distorted from an original by Mencken) that for every complex problem there is an answer that is clear, simple, and wrong.
And there is a fourth, which is perhaps most pertinent of all, which is that for problems of any complexity, technology cannot wish away human behaviour. Even if a contact tracing app were to work perfectly in technical terms (whatever that might mean), the individual and social behavioural responses may be far from what is desired. Or as Anderson puts it:
We cannot field an app that will cause more worried well people to phone 999.
That’s an insight relevant to many more problems than this one.