CNBC's Jim Cramer said on Thursday that investors should pay close attention to the 30-year Treasury yield, which has climbed to roughly 5.3%, as it is the key force currently driving stocks. He explained that a 5.3% return on U.S. government-backed bonds makes them an increasingly attractive alternative to riskier stocks, especially for older investors. Additionally, higher Treasury yields push up borrowing costs across the economy, potentially hindering corporate expansion and slowing economic growth, which could weaken demand and earnings, ultimately impacting stock prices.