The Sensex, India's key stock market index, reflects economic and corporate changes, with inclusion signifying elite status. Companies must continuously prove relevance to remain in the 30-stock index, which is reviewed semi-annually. Over time, many once-prominent companies have faded. Since its 1986 launch, only Reliance Industries, Hindustan Unilever, and ITC have consistently remained in the index, demonstrating resilience and adaptation through various economic shifts.