FinansThe valuation mysterySomething happened to the valuation of US stocks about thirty years ago.The last several decades have just been really strange. They have featured two epic bubbles, a once-in-a-lifetime financial crisis, a revolution in monetary policy and a global pandemic. Maybe it would be unrealistic to expect any market regularities to hold in such a whirlwind.Foto: Vincent Thian/AP/NTBRobert Armstrong (FT)