Demonetisation was not a good idea and the time should have been utilised instead to fine-tune the goods and services tax (GST) before it was introduced, said Gita Gopinath, John Zwaanstra Professor of International Studies and of Economics at Harvard University, in an interview with Advait Rao Palepu. Rising oil prices are emerging as a big challenge for the country, she said while she was in Mumbai to deliver Exim Bank's commencement day lecture. Edited excerpts: