You have certainly heard the expression "blood, sweat and tears," allegedly from a speech Winston Churchill delivered in 1940 at the dawn of war. What he actually said, however, was "I have nothing to offer but blood, toil, tears and sweat." Our collective memories have reduced those four words down to three.
The number three resonates deeply in the human mind, in a visceral, fundamental and pleasing way. There are three primary colors (red, yellow and blue), three wise men, three acts in movies and so on. There is even an old Latin proverb "Omne trium est perfectum," meaning every group of three is perfect.
In business, when it comes to messaging, three items suffice and four are too many, according to experiments with college students conducted by Professor Suzanne Shu from UCLA's business school and Professor Kurt Carlson from Georgetown's. Their seminal article in the Journal of Marketing -- called "When Three Charms but Four Alarms" -- shows that people either discount ads that contain four claims, or disengage entirely. This phenomenon occurs with descriptive materials for shampoo, cereal, candidates and restaurants.
It even applies to "marketing" of potential mates. Shu and Carolson devised an experiment where they asked subjects to imagine a scenario where an old friend from high school mentions that she's dating a guy named John. If she describes him as intelligent, kind, funny and cute, then the listener probably won't be convinced that he's the best partner for her. If she merely says he's intelligent, kind and funny, however, she'll be more persuasive. In this context, cute doesn't matter.
Each successive message adds weight to the argument when you move from one to two points, or two to three, but diminishing returns set in thereafter. If you're tempted to overwhelm your customers with a basketful of messages, don't. Once again, less is more.
The same holds true with quotes. We tend to recall those with three items:
"the government of the people, by the people and for the people"; or "life, liberty and the pursuit of happiness." Julius Caesar's brisk summary of a military campaign in 47 BCE comes to mind too: "I came, I saw, I conquered," which is even more terse in the original Latin: "Veni, vidi, vici." (Notice, I provided just three examples here.)
There is an oddity in the English language that further underscores the force of three. When we indicate the position of items in a series, we use ordinal numbers. Yet first, second and third have unique endings. All others, from fourth to hundredth to nth end in th. Once you go beyond three, everything sounds the same, literally.
Sources:
Suzanne B. Shu and Kurt A. Carlson, "When Three Charms but Four Alarms: Identifying the Optimal Number of Claims in Persuasion Settings," Journal of Marketing, January 2014, pp. 127 - 139. Note: the authors reviewed my article for accuracy.