Diminishing Marginal Utility of Yodeling

One reason demand curves slope downward is that people tend to tire of repetition. This is what Mark Twain discovered hiking in Swiss Alps

The jodling (pronounced yodling,—emphasis on the o,) continued, and was very pleasant and inspiring to hear. Now the jodler appeared,—a shepherd boy of sixteen,—and in our gladness and gratitude we gave him a franc to jodel some more. So he jodled, and we listened. We moved on, presently, and he generously jodled us out of sight. After about fifteen minutes we came across another shepherd boy who was jodling, and gave him half a franc to keep it up. After that, we found another jodler every ten minutes; we gave the first eight cents, the second one six cents, the third one four, the fifth one a penny, contribution nothing to Nos. 5, 6, and 7, and during the remainder of the day hired the rest of the jodlers, at a franc apiece, not to jodel any more. There is somewhat too much of this jodling in the Alps.

[Mark Twain, A Tramp Abroad: Following the Equator, Other Travels, edited by Roy Blount Jr. (New York: Library of America, 2010), p. 187]