What is the policy trilemma?

What will be an ideal response?

The policy trilemma is the hypothesis that it is impossible for a country to have exchange rate stability, monetary policy independence, and free capital flows at the same time. If countries have free capital flows and an independent monetary policy, they must let the exchange rate float. If countries have free capital flows and exchange rate stability, they must give up monetary policy independence. If countries have monetary policy independence and exchange rate stability, they must restrict the flow of capital.