When you ask people for help with projects or tasks, how likely are they to do what you ask? It turns out that one factor tips the balance between likely to help you or unlikely – whether you thanked them last time they did.

It may seem obvious that thanking someone for a favor makes them more willing to do another one, but you might be surprised at how big a difference it makes.

That insight comes from Wharton psychologist and New York Times bestselling author Adam Grant. In a LinkedIn post about email, Grant describes a study he did along with Francesca Gino, a professor at the Harvard Business School.

Researchers asked people to help a student improve a job application letter. In some cases, the students (who were following the researchers' instructions) wrote back simply to let the person know that they'd received the feedback.

In other cases, they responded, "Thank you so much. I am really grateful." Then, three days later, the same students asked for help again.

You could probably guess that the students who said thank you were more likely to get help a second time. But you might be surprised at how much more.

When the non-thanking group of students asked for more help, only 32 percent got help again. When the thanking students asked, 66 percent got a second helping of help.

People were more than twice as likely to help someone who'd thanked them than someone who hadn't. To put it another way, the majority of people in the study would help someone a second time if they said thank you the first time, but not if they didn't.

Why is "thank you" so powerful?

Here's what I find really fascinating. The experiment had been designed to answer a simple question that we don't often ask: Why exactly does thanking someone make them likelier to help again?

I would have guessed that expressing gratitude makes the other person feel valued and good about themselves – a feeling that they hope to have again when they help someone the next time. But that guess would be wrong.

This research shows that what actually happens is something much more important. Thanking people makes them feel more "socially valued" – more connected to other people around them and their community as a whole. That increased sense of connection is a very, very powerful thing.

Just how powerful it is became clear in a second phase of the study, where the follow-up request for help came from a different student from the first. There was no reason for the subjects to feel particularly connected to this new student since they hadn't interacted before.

Nevertheless, if the first student had thanked them, they were still more than twice as likely to provide help a second time.

Think about what this could mean for your company or your team. By encouraging people to thank each other every time they get help from another team member or partner, you can foster that "prosocial" feeling that makes people likelier to help one another throughout the whole group.

That would lead to more people thanking each other, making them likelier to provide more help in the future and on and on in a virtuous cycle.

There's a growing audience of Inc.com readers who receive a daily text from me with a self-care or motivational micro-challenge or tip. Often they text me back and we wind up in a conversation. (Want to learn more?

Here's some information and a special invitation to an extended free trial). Many are entrepreneurs or business leaders and they tell me how vitally important that sense of community and helping each other is for every aspect of success in both business and life. Who could have guessed this simple two-word phrase is such a powerful way to make it happen?

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