Diminishing returns: the fridge timetable with no empty box

The timetable on Meera's fridge has no empty box left. Maths on Monday, science on Tuesday, English on Thursday, and a test series every Sunday. Her son Aarav is in Class 10 in Nagpur, and his marks have not moved since the second tuition. He is only more tired.

Nobody is to blame here. Meera added each class for a good reason, and the first one really did help.

What the model is

Diminishing returns means that each extra unit of the same thing gives less than the one before it. The idea goes back to the economists Turgot and David Ricardo, who both thought about it through farming. Put the first bag of seed on a field and the harvest jumps. Put a tenth bag on the same field and it adds very little.

It does not say the extra effort is useless. It says the next unit is worth less than the last one, and at some point it can cost more than it gives.

The timetable, step by step

Meera takes a sheet of paper and makes three rows, one for each tuition. For each she writes two things: what it added, and what it costs.

The first class fixed the basics, and Aarav's maths test came back clearly better. The second class added a little: he now finishes the paper on time. The third class adds nothing she can point to. It costs ₹2,000 a month, five hours a week, a long ride in the evening heat, and the Sunday he used to spend sleeping or sitting with his cousins.

She does not decide that night. She asks Aarav which class he actually gets something from, and she asks his teacher what he still needs. She also notices something simple. The marks stopped moving where the added classes started covering the same ground again.

The same shape shows up elsewhere. A third streaming subscription gives you another list of shows you will not watch. One more hour of overtime at the end of a long day may produce less work than the first hour did.

Where it goes wrong

Diminishing is not the same as zero. The last class may still matter in exam week, and one flat test is not proof that it did nothing. Marks also move for many reasons, so a pause in them is a hint, not a verdict.

The model also does not say "stop trying". It asks where the next hour or rupee would give more. Sometimes the answer is sleep, or an hour of revising alone, or nothing at all.

One thing to try today

Pick one thing you keep adding to: classes, subscriptions, extra hours, another app on the phone. Before tonight, write two lines on paper. What did the last addition give you? What did it take from you?

This is a way to think, not financial, medical or legal advice.

Each Sunday: one mental model and one real decision to try it on. Find more in the /models library.