New Delhi, Feb. 20 -- When the US stock market today responds to global capital flows and the rupee edges closer to 90 against the dollar, the reaction is always the same: alarm, debate, and a rush to explain why this time feels different. But the truth is quieter, and far more consequential. For most long-term investors, the real cost of currency depreciation is not felt in the year it happens. It shows up years later, when portfolios look respectable on paper but feel insufficient in practice.

The rupee near 90 is not a sudden shock. It is the visible end of a long, structural slide. In 1991, the rupee averaged around Rs.22.74 to the dollar. By 2001, it was closer to Rs.47.19. In 2011, it briefly strengthened to the mid-40s before resu...