As investor enthusiasm for artificial intelligence, and lately for a Trump Presidency, has been driving the stock market to record highs this year, Jeremy Grantham has been having flashbacks. At the end of the nineteen-nineties, the veteran value investor--one that looks for undervalued stocks--shied away from soaring Internet and technology stocks, believing that their prices had departed from financial reality, and that the market was heading for a crash. Far from thanking him for sounding the alarm, many clients of G.M.O., a Boston-based investment-management firm that Grantham had co-founded, held it responsible for making them miss out on a vertiginous rise in the Nasdaq, which went up by about a hundred and sixty per cent between 1998 and 1999. Some withdrew their money from the company. "We started off in a good position, and in two years we lost almost half of our business," Grantham recalled.