This is from Gilbert Krebs. The author is not known.

In the wealthy suburbs of a city, a strange malady was striking the gardeners on the large estates. They were becoming very morose and depressed, and had to be hospitalized. The first signs of the disease were when they started complaining that the lawns were in terrible shape. A psychiatrist brought in to find out what was happening noticed that there were some gardeners who still remained cheerful and never developed the lawn-hating symptoms. The psychiatrist went over and over this group, trying to find out why they were immune and what they were doing differently. Finally, he noticed that the healthy gardeners always had garden twine in the wheelbarrow, whereas the sick gardeners carried the roll in their pockets. So then the cure was obvious: “Walk on, walk on, with rope in your cart, and you’ll never knock a lawn.”