Fable
The proportions of herbs in a pharmacy's formula
The South City apothecary had a large medicine pot, specially for training apprentices to identify prescriptions. The master put samples of mountain herbs, seaside shells, common pills and powders from the city, and several rare poisonous herbs into the library, and had the apprentices identify them daily according to prescriptions.
At first, the master, looking to save effort, dumped in baskets full of the most common cold remedies and trauma remedies. The apprentice learned fast, and whenever an ordinary customer came in, he could fill the prescription immediately. But when a rare symptom appeared, he either failed to recognize it or mistook a rare poisonous herb for an ordinary heat-clearing one, nearly causing disaster. The first time, the master looked only at the overall accuracy rate; ordinary prescriptions were the majority, so the numbers looked great. Only when the rare poisonous herb caused an error did he realize that the minority but high-risk samples had been hidden by the average.
Someone suggested dumping all the rare herbs in. A few months later a new problem appeared: the apprentices memorized strange prescriptions every day, yet couldn't even be sure about the most common cough and cold. The shop seemed more knowledgeable, but its actual counter service became less reliable.
Only then did the master rearrange the medicine storage. He placed common formulas according to the real proportions of visitors, and reserved fixed practice slots for high-risk, high-cost medicinal materials; overly similar medicines had to be compared on alternate days, and rare but critical medicines had to be given heavier assessments. After each practice session, he also looked at which types of formulas the apprentices often got wrong, then adjusted the next batch of samples. Rearranging the medicine storage was not a one-time task either. After winter set in, cough and asthma visitors increased, and in spring eczema became more common; if the proportions in the medicine pot did not move with the seasons, the apprentices' feel would drift again.
The apprentice discovered that the materials in the medicine pot were not better the more there were, nor better the rarer they were. The source, proportion, repetition count, and difficulty of the materials together shaped his feel. If one ingredient was added too much, the other flavors were masked; if a certain type of illness never appeared, he would be blind when standing at the counter. Some sources also conflicted with each other. In the city, pills and powders were written in neat forms, while mountain herbs had chaotic names; without cleaning and labeling, the apprentice would mistake differences for medicinal properties.
The apothecary finally left a rule: compounding a practice remedy is not grabbing a handful from the warehouse at random, but balancing the scales among various sources. When the scales are balanced correctly, the apprentice neither over-specializes nor gets led astray by a few noisy samples.