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Notes: David Mashiah

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The bouquets got better and sales fell

Shelf life went from half a week to 14–21 days and sales fell anyway. Customers could see the size of a bouquet. They could not see the freshness.

The training set moves the error 390x. Nothing predicts it.

Across 231 training-set choices the worst case moved by a factor of 390. I tested nine cheap ways to pick a good one. None of them held up.

The metric was measuring my model, not the problem

A transferability score held at 0.54 across two independent budgets, then collapsed to 0.14 when I changed the model class. It was tracking the algorithm.

You cannot count the sale you did not make

Sales data records what you sold, not what people wanted. The two differ exactly on the days they matter most, and the gap teaches a forecast to shrink.

A scratched label still scans, and that is not luck

A check digit tells you a barcode scan was wrong. Reed–Solomon parity tells you what it should have been. That difference decides what a damaged label costs.

Why a screen cannot measure vernier acuity

A screen pixel at 60 cm subtends about 90 arcseconds; clinical vernier thresholds are 2–5. Antialiasing still measures below one pixel. Here is the arithmetic.

My model scored perfect and that was the problem

A perfect held-out score measured one thing: whether the model could repeat what it had seen. Of 30 cross-family tests, 20 fell below a crude baseline.