From: The Patrician To: Directors of Purple Lantern Ltd.¶
To the Directors of Purple Lantern Practice Ltd.,
I find it prudent to clarify why your firm has been retained, as misunderstandings tend to multiply when left unattended, rather like mould in municipal archives.
Scarlet Semaphore was authorised to test the city’s assumptions about its routing, its controls, and its collective attention span. They have done so with enthusiasm, creativity, and a commendable disregard for the comfort of others. This was expected.
The Department of Silent Stability was instructed to observe, not intervene. They have complied, largely by observing everything except the precise moment when intervention might have been useful. This was also expected.
What neither party is well suited to do is to tell me, repeatedly and reliably, what these activities mean for the continued functioning of the city.
Scarlet Semaphore produces incidents.
Silent Stability produces explanations.
Neither reliably produces understanding.
This is where you come in.
Purple Lantern Practice Ltd. has been engaged to construct a simulator not as a toy, nor as a demonstration, but as an instrument of civic hygiene. The city cannot afford to relearn the same lesson every time a different clerk presses the wrong button, or a different operator assumes that best practice was followed because it was written down.
Your task is therefore threefold.
First, to take the abstract attack trees that decorate all our shelves and turn them into concrete sequences of actions that a human being might actually perform under time pressure, fatigue, and budgetary constraint.
Second, to translate those actions into observable effects, complete with ambiguity, noise, and plausible deniability, so that our defenders may practise recognising trouble before it announces itself loudly.
Third, and most importantly, to ensure that Scarlet Semaphore and the Department of Silent Stability are both forced to confront the same shared reality, rather than their preferred versions of events.
Scarlet Semaphore must see that cleverness leaves traces.
Silent Stability must see that traces do not arrange themselves helpfully.
I must see whether the city survives either way.
The simulator is not intended to prevent failure. Failure is inevitable and, within limits, educational. It is intended to prevent surprise, which is expensive and politically inconvenient.
You will keep your work independent of both departments. You will listen to them carefully. You will believe neither of them completely.
If this arrangement causes discomfort, then it is functioning as designed.
Should you succeed, the city will be quieter, which is how I prefer it. Should you fail, the city will be louder, and I will have further questions.
I trust this clarifies matters.
Yours,
Havelock Vetinari, Patrician of Ankh Morpork
Acting Head of Everything That Eventually Becomes My Problem