Are Economists Pessimists by nature?

In the paper
Reconsidering Expectations of Economic Growth after World War II from the Perspective of 2004 by Robert W. Fogel - University of Chicago, GSB, explains how many economists of the 19th and 20th centuries have been pessemistic about the growth of The world economy...here is an interesting quote from his paper.

The economists in 1850 wrote that the progress of
the last decade had been so great that it could not possibly continue. And economists at
the end of the nineteenth century wrote that the progress of the last half century has been so great that it could not possibly continue during the twentieth century.

Will they be proven wrong again?