Why is retiring at 55 with ₹80 lakh in FDs not enough?

For a 55-year-old person with current monthly expenses of ₹60,000, retiring with an ₹80 lakh investment in fixed deposits may not be enough, as per Moneycontrol. To sustain ₹80,000 monthly for 20 years (given 6% inflation and life expectancy stretching to 75), assuming a 6.5% FD return, required corpus hits ₹1.83-crore. The ₹80-lakh corpus covers only 44%-46% of retirement needs.