Irving Fisher was a noted 20th century economist. No less an authority than Milton Friedman called him "the greatest economist the United States has ever produced," and many of his contributions to economics, such as the Fisher equation, the Fisher hypothesis and the Fisher separation theorem are cited by economists to this day.
Yet despite his intellect, he made one statement in 1929 that destroyed his credibility for the rest of his life.
Three days before the Wall Street Crash of that year, he claimed that, " s tocks have reached what looks like a permanently high plateau." When he was disproved 72 hours later, he tried to get out from under the statement, but months of putting a positive spin on developments only further eroded his reputation. He died in 1947, but a renewed interest in neoclassical economics in the 1950s caused a re-evaluation of his work and a rehabilitation of his name.