These are shapes rather than industries — the same shape turns up in a warehouse, a payroll run and a lettings office. One note on how to read them. Everywhere else on this site the third line under each item says what breaks if you do not have the thing being described. Here it is inverted: it says what breaks if you use a model on this shape anyway.
01The rule is already written
Deterministic logic, decision tables, rules engines, validation at the point of entry
If a policy can be stated as a table — orders above this value from customers in that band get this rate, unless the account is on stop — then it is already a program. Somebody has done the difficult part, which was deciding the rule. What remains is typing it into a decision table or a page of code, where a non-programmer can read it, where it can be unit tested, where every change is in version control with a name and a date against it, and where an auditor asking why one order was priced that way gets the rule itself as the answer. A model asked to apply the same rule will get it right most of the time. Most of the time is a weaker guarantee than the one you already had, at a higher cost per invocation and with a slower answer.
You have replaced a rule anyone can read with a system nobody can read, and taken on an evaluation programme to establish something the decision table gave you for nothing — that the rule is applied correctly on every single case rather than on the ones you sampled. When the policy changes, you now retest a model instead of editing one line and shipping it before lunch.
02The answer must be identical every time
Determinism, exact decimal arithmetic, reproducibility, calculations subject to audit
Payroll deductions, VAT, interest accrual, commission splits, duty and unit conversions in a regulated environment. Two properties matter in this work and a language model has neither of them. The first is reproducibility: the same input must give the same output on every run, including the run someone repeats eighteen months later because an employee has queried a payslip. The second is exactness: money is decimal arithmetic with defined rounding, and a system predicting the next token is not performing decimal arithmetic even when it prints a number that looks plausible. A model can be genuinely useful next to this work — reading the timesheet, pulling figures off a supplier invoice, explaining to an employee in plain English why their deduction changed this month — but the calculation itself belongs in code, with the rates held as data so they can be changed without a release.
You turn a number that has to be defensible into a number that has to be checked. An error of a penny in a rounding rule does not announce itself; it accumulates quietly across a few thousand payslips until somebody notices, and by then you are reconstructing months of runs that cannot be reproduced. The model generated it is not an answer that satisfies an auditor, a regulator or the person holding the payslip.
03The data isn't there yet
Data capture, provenance, ground truth, the judged examples nothing can be evaluated without
This is the most common one we see, and the least welcome. The proposal is a model that predicts something valuable — which machine is about to fail, which invoice will be paid late, which shift will be short-staffed — and the records that would ground or train it either do not exist, exist in three systems that disagree about the same event, or exist as free text in a comments box that four people fill in four different ways. Ground truth is the term for what you would compare the model's answers against: real cases, judged by somebody qualified, held aside and used for nothing else. Without it there is no way to tell a good system from a confident one. A fortnight spent making the warehouse scan the barcode at the moment the pallet actually moves, or adding one required reason code to a form, buys more than any model built on the records you have now — and it is the precondition for the model you build next year.
You get a system that is confidently wrong in precisely the pattern of your existing data problems, and no means of proving it, because the ground truth you would measure against is the thing you did not have. It will look fine in the demonstration, where the records were chosen by hand, and it will disappoint on the first week of real traffic in a way nobody can diagnose.
04The volume doesn't justify it
Cost per call, build cost amortised across usage, the person-minutes actually displaced
Do the arithmetic before the architecture. Count how many times the task happens in a month, multiply by the minutes a person spends on each one, and set that against the build cost, the per-call cost of the model, and the standing cost of somebody owning the thing — because an AI system in production has an owner, a monitoring dashboard and a bill, permanently. A task that happens forty times a month and takes four minutes is under three hours of work a month. There is almost nothing worth building there, and a checklist or a better form will beat anything we could ship. The same task at four thousand times a month is an entirely different proposition. Volume is not the only multiplier that counts: a rare task can be worth automating when being slow at it is expensive, as with a safety recall or a bid deadline. But that is a case you should be able to state out loud in one sentence before anyone starts.
You spend more building and running the system than the work it replaced ever cost, and the loss is a quiet one. It does not surface as a failure anybody reports. It surfaces as a line in a cloud bill and as an engineer's attention held permanently by a system that saves three hours a month.
05The process itself is the problem
Process design before automation; the failure mode where speed multiplies a defect
Some processes are slow because they are broken. An approval step exists because two departments do not trust one another. A form has twenty fields of which four are ever used, and a person downstream spends their morning working out which four mattered this time. A reconciliation runs every Friday only because two systems were never integrated and both hold a version of the same order. Automating any of these preserves them exactly as they are. It also removes the friction that was, quietly, the only reason anyone still noticed how bad they were — a step that hurts gets fixed eventually, a step that has been made effortless never does. The right move is a fortnight of process work: delete the step, integrate the systems, cut the form to four fields. What remains afterwards is often small enough that the automation question answers itself.
You make a bad process fast, which means it produces its bad outputs faster than anybody can review them, and errors that used to be caught by the slowness now travel all the way to a customer. The automation also encodes the broken process in software, so fixing the process properly later stops being a conversation and becomes a rebuild.