SCARLUS is a mnemonic I came up with a few years ago for the seven principles of influence from Robert Cialdini’s research: Scarcity, Consistency, Authority, Reciprocity, Likeability, Unity, and Social proof. Each one describes a shortcut people use to decide, and each can be applied ethically to persuade.

Scarcity

People want more of what is rare or dwindling. Perceived scarcity raises perceived value.

Example: “Only 3 spots left in the cohort” drives sign-ups far harder than “spots available.”

Consistency

People strive to act in line with their prior commitments and self-image. Small commitments pave the way for larger ones.

Example: Someone who publicly agrees a cause matters is far more likely to later donate to it.

Authority

People defer to credible experts and legitimate signals of expertise. Credentials, track record, and confidence all carry weight.

Example: “Recommended by 9 out of 10 dentists” moves product because dentists are the authority on teeth.

Reciprocity

People feel obligated to return favors, gifts, and concessions. Give first, and give something genuinely valuable.

Example: A free sample or free useful advice makes the recipient far more likely to buy or help later.

Likeability

People say yes to those they like. Similarity, genuine compliments, and cooperation build liking fast.

Example: A salesperson who finds real common ground with a customer closes more deals than one who goes straight to the pitch.

Unity

People are swayed by those they share an identity with. “One of us” is more powerful than “one like us.”

Example: “As fellow MIT founders, we should stick together” lands differently than any appeal from an outsider.

Social Proof

People look to what others are doing to decide what is correct, especially under uncertainty. The more similar the others, the stronger the pull.

Example: “Most guests reuse their towels” outperforms environmental appeals in getting hotel guests to reuse theirs.

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