“The soil in return for her service / keeps the tree tied to her, / the sky asks nothing and leaves it free.” – Rabindranath Tagore (“Fireflies,” 1928)

In “The Psychology of Persuasion”, Robert Cialdini tells the story of a university professor who was interested in how deeply people feel about reciprocity — how strongly they feel about paying back debts.

This professor had a theory that feeling indebted is such a psychological burden that people given unasked-for kindnesses often feel compelled to return them. He tested this principle by sending Christmas cards to a group of strangers. As he expected, a very large number of them sent holiday cards back to him.

Why did these people send cards back to a man they didn’t know? The professor believed it was because they felt a moral obligation to do so. The card was a little gift — and gifts create a sense of obligation. The easiest way to discharge this obligation was to send a card back. The two cards canceled out the moral IOUs and then life could go on without further commitments.

In other words, when someone does us a favor, we feel that we “owe” him a favor in return. Conscientious people like to unburden themselves of obligations as soon as possible — and that seems to be especially true if the favors are owed to strangers.

There are numerous studies that demonstrate how this works in social situations. Cialdini reports many in his book. But the one that has probably had the greatest effect in terms of making money involves the Hare Krishna people.

You probably know about the Hare Krishnas. You may have seen them walking down the street together or clustered in airports or train stations. They dress in white and peach-colored robes and are fond of shaving their heads. They play little cymbals and chant, “Hare Krishna, Hare Krishna, Hare Hare, Krishna Krishna.” They seem to be a happy cult. They smile. They beg.

According to Cialdini, their beggingwas netting them very little money before they discovered the secret of reciprocity. One day, one of them came up with a very smart idea. “Before we ask for anything,” he might have said, “let’s give them something, like a flower.”

They realized that by giving first they would change the relationship from one of beggar/donor to one of creditor/debtor. They tried various gifts — cards, booklets, and so on — but flowers seemed to work best. This unique use of the reciprocity secret single-handedly caused the Hare Krishna organization in the United States to grow from an insignificant fringe cult to a billion-dollar enterprise.

This same technique has been used very successfully through direct mail by the Republican Party, several charities, and many survey groups. In these cases, the trick has been to include a dollar bill in the solicitation as a “gift” for taking the time to read the letter (or fill out the survey). The dollar insert triples the cost of the mailing (which is usually about 50 cents), but the response is so much greater — because recipients feel compelled to reply — that it more than makes up for the extra expense.

The concept of giving someone a present before asking for a favor is so strong and so universal in its potential applications that I’m tempted to say no effort to persuade, to motivate, or to sell should be made without it.

Think about the possibilities.

What if you were running an upscale retail store selling suits for men and every time a new customer came in, rather than ignoring him or (possibly worse) confronting him with “How can I help you?” you came to him with a cup of espresso or tea on a silver tray? Wouldn’t he be much more inclined to buy from you?

What if you were a door-to-door vacuum-cleaner salesperson and started your presentation by giving the prospect a basket full of free cleaning goodies (brushes, sponges, etc.)? Wouldn’t you close more sales?

Or what if you were a freelance professional, such as a writer or graphic artist, and began each new business relationship by giving your new client a beautiful pen, a framed lithograph, or perhaps a book or pamphlet you wrote? What business relationship wouldn’t start better with a gift?

Purchasing agents — people whose job it is to buy goods and services for companies — are often prohibited from accepting gifts. There is a good reason for that: Gifts work! In fact, the psychological demand to repay a gift is so strong that recipients will often spend 10 or 100 or even 1,000 times the cost of the gift to square things up.

It seems to me that there is almost no sales or marketing situation in which some clever use of the reciprocity principle wouldn’t boost response. The same thing can probably be said for most social and personal situations.