What Became of the Liquidity Trap?

"Over half a century ago at Oxford, when along with my research appointment I was also doing some teaching, I had an Indian student who was a graduate of an Indian university but, for reasons of prestige, came to read an undergraduate course. Once I gave him an essay to do on the Natural Rate of Interest. At his next tutorial, he read out aloud an immensely complicated and confused text that I did not comprehend and I was sure that he did not either. I gathered all my forces of didactic persuasion and explained to him, or I thought I had, where he had gone astray and how the problem can be reduced to its essentials. Then, exhausted, I sat back, proud of myself and full of admiration for the quality of Oxford teaching of which I have just shown such a glowing example."