Monotony, the cardinal and most common sin of the public speaker, is not a transgression—it is rather a sin of omission, for it consists in living up to the confession of the Prayer Book: “We have left undone those things we ought to have done.”
Emerson says, “The virtue of art lies in detachment, in sequestering one object from the embarrassing variety.” That is just what the monotonous speaker fails to do—he does not detach one thought or phrase from another, they are all expressed in the same manner.
To tell you that your speech is monotonous may mean very little to you, so let us look at the nature—and the curse—of monotony in other spheres of life, then we shall appreciate more fully how it will blight an otherwise good speech.
If the Victrola in the adjoining apartment grinds out just three selections over and over again, it is pretty safe to assume that your neighbor has no other records. If a speaker uses only a few of his powers, it points very plainly to the fact that the rest of his powers are not developed. Monotony reveals our limitations.
In its effect on its victim, monotony is actually deadly—it will drive the bloom from the cheek and the lustre from the eye as quickly as sin, and often leads to viciousness. The worst punishment that human ingenuity has ever been able to invent is extreme monotony—solitary confinement. Lay a marble on the table and do nothing eighteen hours of the day but change that marble from one point to another and back again, and you will go insane if you continue long enough.
Project Gutenberg–a library of online/ebook public domain works–is amazing. Why else would you casually come across books published over a century ago like The Art of Public Speaking by Dale Carnagey and J. Berg Esenwein.