Just as relevant today as it was in 1940:
“…it is important to note that mass speculation can flourish only in such an atmosphere of illogic and unreality. The self-deception of the mass speculator must, however, have its element of justification. This is usually some generalized statement, sound enough within its proper field, but twisted to fit the speculative mania. In real estate booms, the “reasoning” is usually based upon the inherent permanence and growth of land values. In the new-era bull market, the “rational” basis was the record of long-term improvement shown by diversified common-stock holdings.” –Ben Graham and David Dodd, Security Analysis
Today’s “element of justification” probably relates to what the Fed is doing and is perceived will do if the economy softens, and the majority’s belief in what that means for stock prices.