Goldman's top equity strategist tells BI 2 similarities between today's market and the dot-com bubble -- and what it means for your portfolio

David Kostin of Goldman Sachs warns of similarities between today's market and the dot-com bubble, with high market concentration and valuation gaps posing risks. He predicts lower returns for the S&P 500 and advises investors to consider mid-cap and equal-weighted index options for better performance.