Ideas grouped in threes are more memorable and more persuasive than in other quantities.
Classical rhetoric's tricolon. Caesar's veni, vidi, vici and Lincoln's of the people, by the people, for the people are the standard examples, and the pattern holds across languages.
In practice
- A safety briefing with three instructions is followed; the same briefing with nine is signed for.
- A pitch with three reasons is remembered; the same pitch with six is remembered as having had several.