Reciprocation tendency
We feel compelled to return favours and injuries in kind.
Cialdini's bedrock principle. When someone does something for us (a small gift, a favour, a piece of information), we feel a strong psychological pull to do something for them in return. The same applies in the negative direction: we feel compelled to retaliate against injuries.
This is what makes "free" samples, gifts to journalists, and small acts of generosity in B2B sales work. The recipient doesn't consciously feel obligated; they just experience a vague pull to reciprocate that's hard to resist.
The defence: when someone gives you something unsolicited that feels designed to obligate you, recognise the dynamic. You're under no obligation to reciprocate just because they triggered the instinct. The trick is to notice the pull rather than act on it automatically.
Examples in the wild
Pharmaceutical reps used to give doctors small gifts (pens, dinners). Studies showed doctors who received gifts prescribed the giver's drugs at higher rates, even though they would have denied any influence. The effect was real.
Investment bankers cultivate relationships with potential clients through years of small favours. The reciprocation instinct often produces deals at the right moment without any explicit ask.
Birthday gift escalation in friendships is reciprocation gone wrong. Two friends each try to slightly outdo last year's gift, and within a decade everyone hates birthdays.
Reciprocation tendency is one of the mental models we apply through real cases inside the Pareto MBA — a part-time program for professionals who want to think clearly about business.