What's been India's biggest selection blunder of the year?

On their tours of South Africa, England and Australia in 2018, India have made several debatable selections in their playing XIs. Virat Kohli, the captain, and Ravi Shastri, the coach, have tried to pick sides for specific conditions and have given importance to recent form over reputation, but their choices have not always paid off. Which of these decisions do you think was the biggest mistake?