Background
Arizona State University social psychologist Robert Cialdini described himself as a lifelong "patsy" who couldn't say no. To learn how professional persuaders work, he spent three years undercover in car dealerships, telemarketing firms, and fundraising organizations. He combined those field observations with lab experiments in Influence (1984), which has sold millions of copies and become a staple of marketing and negotiation. In Pre-Suasion (2016) he added a seventh principle, unity: people are more easily persuaded by someone who shares their identity as "one of us."
The six principles
Reciprocity: we repay what we receive, which is why free samples work and mints with the bill raise tips. Commitment and consistency: small agreements lead to bigger ones (the foot-in-the-door technique), driven by the wish to avoid cognitive dissonance. Social proof: we follow what others do, akin to the bandwagon effect. Liking: we say yes to people we like. Authority: we defer to experts and uniforms. Scarcity: "limited stock" makes things more desirable. In a famous hotel experiment, a sign saying most guests in that room reused their towels beat environmental appeals by a wide margin.
Use and defense
The principles show up everywhere in marketing, from review counts and flash sales to expert endorsements and word of mouth. They often work alongside biases like anchoring and framing. Cialdini stresses that faking them, for example with false scarcity or fake reviews, is unethical. A simple defense is to pause and ask: am I deciding because of the product itself, or because of the scarcity or authority cue?
FAQ
- Which principle is most powerful?
- It depends: social proof dominates under uncertainty, and scarcity when a loss is at stake.
- What is the seventh principle?
- Unity, added in 2016—people are more persuaded by those they see as part of their group.
Sources reviewed: 2026-10-26
References
- Cialdini, R. B. (1984). Influence: The Psychology of Persuasion. William Morrow.
- Cialdini, R. B. (2016). Pre-Suasion. Simon & Schuster.
- Goldstein, N. J., Cialdini, R. B., & Griskevicius, V. (2008). A room with a viewpoint: Using social norms to motivate environmental conservation in hotels. Journal of Consumer Research, 35(3), 472–482.