Heavily involved in the market himself, he too surrendered to the basic speculative impulse

A Short History of Financial Euphoria by John Kenneth Galbraith.  Page 79.

The most prominent and most to be regretted of the academic sages was Irving Fisher of  Yale - as already indicated, the most innovative economist of his time. Heavily involved in the market himself, he too surrendered to the basic speculative impulse, which is to believe whatever best serves the good fortune you are experiencing. In the autumn of 1929, he gained enduring fame for the widely reported conclusion that "stock prices have reached what looks like a permanently high plateau."

There was also optimistic expression from Harvard, Michigan, Ohio State, and notably from a young Princeton economist, one Joseph Stagg Lawrence, who, as stocks reached their peak, offered the widely quoted comment, "The consensus of judgment of the millions whose valuations function on that admirable market, the Stock Exchange, is that stocks are not at present overvalued." He added the question, "Where is that group of men with the all-embracing wisdom which will entitle them to veto the judgment of this intelligent multitude?"

A few did, and they did not escape articulate and even savage denunciation. As earlier noted, Paul M. Warburg, who, at least until he spoke out against the market, had been one of the most respected bankers of his time, was especially condemned, as was the equally well-known, if somewhat less reputable, Roger Babson.