F.H. Clauser 1967 (from a study group report at the National Academy of Sciences), quoted from Richard Rhodes, Visions of Technology.
In years gone by, studies aplenty have been made foretelling the future trends of speed and size of aircraft, powers and weights of engines, range and capabilities of radars, and so on. Occasionally, some devilish individual takes the trouble to go back and compare past predictions with later reality. Invariably, he finds that engineers and scientists are a conservative lot in their predictions. The immediate problems that confront them appear so formidable that they flinch from predicting ever-accelerating progress and conjure up visions of a natural barrier ahead which will cause the curve of progress to flatten off much as a biological population comes into equilibrium with its environment.