"We have already seen, in the previous chapter, another example of people who had lucrative opportunities to save but did not use them: the fruit vendors from Chennai, who borrowed about 1,000 rupees ($45.75 USD PPP) each morning at the rate of 4.69 percent per day. Suppose that the vendors decided to drink two fewer cups of tea for three days. This would save them 5 rupees a day, which could be used to cut down on the amount they would have to borrow. After the first day with less tea, they would have to borrow 5 rupees less. This means that at the end of the second day, they would have to repay 5.23 rupees less (the 5 rupees they did not borrow, plus 23 paisas in interest), which, when added to the 5 rupees they saved that second day by again drinking less tea, would allow them to borrow 10.23 rupees less. By the same logic, by the fourth day, they would have 15.71 rupees that they could use for buying fruit instead of borrowing. Now, say they go back to drinking their two cups more tea but continue to plough the 15.71 rupees they had saved from three days of not drinking so much tea back into the business (that is, borrowing that much less). That accumulated amount continues to grow (just as the 10 rupees had turned into 10.71 after two days) and after exactly ninety days, they would be completely debt-free. They would save 40 rupees a day, which is the equivalent of about half a day’s wages. All just for the price of six cups of tea! The point is that these vendors are sitting under what appears to be as close to a money tree as we are likely to find anywhere. Why don’t they shake it a bit more?"
From "Poor Economics: A Radical Rethinking of the Way to Fight Global Poverty"
https://www.amazon.com.au/Poor-Economics-Radical-Rethinking-...