Things which appear in threes seem to be more easier to remember, more persuasive and satisfying. What’s more, coming up with three things, ideas or phrases in your statement will be more catchy as you bring a rhythm to it.
It’s also known as rule of three and the Latin phrase omne trium perfectum (everything that comes in three is perfect, or, every set of three is complete) conveys the same idea as the rule of three.
It’s widely used as rhetoric, punchline, advertisement campaigns etc..
Example
>Life, Liberty and the Pursuit of Happiness – Rights outlined in the U.S. Declaration of Independence
>Liberté, égalité, fraternité (Liberty, Equality, Fraternity) – The slogan of the French Republic predating 1790
>Veni, vidi, vici (I came, I saw, I conquered) – A triad popularly attributed to Julius Caesar of Rome
>“Government of the people, by the people, for the people – Abraham Lincoln