Cuando la gente actúa al unísono, no solo se ven a sí mismos como más parecidos, sino que después se evalúan unos a otros más positivamente. - Robert B. Cialdini

A well-known principle of human behavior says that when we ask someone to do us a favor we will be more successful if we provide a reason.

Once again we can see that social proof is most powerful for those who feel unfamiliar or unsure in a specific situation and who, consequently, must look outside of themselves for evidence of how best to behave there.

It is much more profitable for salespeople to present the expensive item first, not only because to fail to do so will lose the influence of the contrast principle; to fail to do so will also cause the principle to work actively against them. Presenting an inexpensive product first and following it with an expensive one will cause the expensive item to seem even more costly as a result — hardly a desirable consequence for most sales organizations.