One time when I was going away on a short vacation, I did something really dumb: I parked my car in the short-term parking. This may not seem immediately foolish, but think about it: I was going away for 12 days and my car was racking up the fees by the hour.

I immediately called my roommate Kurt and asked him to move my car for me. I promised I'd owe him big time, and that he'd be able to collect whenever he chose.

Kurt whipped through his remaining work day, rode his bike home, got his car, and drove to the airport. Once at the airport, he parked his car in the long-term parking, took the shuttle to short-term parking, got my car, took it to short-term parking, and drove his car home.

Now, whenever Kurt needs me to do him a favor, he doesn't even have to say the words, "You said I could use the airport incident any time" for me to do him a favor. I'm in his debt and I'm happy to return that favor whenever I can.

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In a 2015 interview, Robert Cialdini, author of the book Influence: The Psychology of Persuasion, explained that he believes there's an easy way to get someone to give you what you need.

How? By doing something useful for them first.

Cialdini calls this the rule of reciprocity. 

What is the rule of reciprocity? The rule of reciprocity refers to a social norm of an instance where someone does something for you, and you then feel obligated to now do something for them in return.

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Reciprocity can have a powerful impact on our behavior, as it can also be seen as a beneficial and positive thing for us as a society. It allows us to develop a give-and-take mindset with the people in our lives.

He explained, "People will help if they owe you for something you did in the past to advance their goals. Get in the habit of helping people out, and — this part’s really important — don’t wave it away when people thank you. Don’t say, 'Oh, no big deal.'

We’re given serious persuasive power immediately after someone thanks us. So, say something like, 'Of course; it’s what partners do for each other' — label what happened an act of partnership. With that prework done, a manager who subsequently needs support, who needs staffing, who maybe even needs a budget, will have significantly elevated the probability of success." 

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I don't think the thing you do for another person specifically has to do with goals — just helping someone else out works.

In fact, in one 2002 study, researchers found that waiters received larger tips if they gave their customers a mint along with the bill. When the waiters paused, made eye contact with the customer, and gave them a second mint, the tip went up by a huge 20 percent.

The researchers concluded that people felt obligated to return the generous gesture, even if they didn't specifically request that the waiter bring them candy.

As long as you aren't sacrificing anything, it's never a bad idea to be helpful and do things for people. You never know when you'll be able to collect that favor.

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Christine Schoenwald is a writer, performer, and frequent contributor to YourTango. She's had articles featured in The Los Angeles Times, Salon, Bustle, Medium, Huffington Post, Business Insider, and Woman's Day, among many others.