If anything, it's giving and not receiving that makes us value a friend more. It was the American statesman and inventor Ben Franklin who first observed the paradox, now called the Ben Franklin Effect: "He that has once done you a kindness will be more ready to do you another than he whom you yourself have obliged." In a nutshell, while material favors don't even come close to the emotional talents of our friends, we still want to validate our personal judgment by investing special qualities in those we select to help.

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Fortunately, studies show that physical proximity has little effect on the ability to keep a friendship in working order. Moving to another state is not the friendship death knell it once was, thanks to the Web. Between e-mail and cell phones with free long distance, we're able to stay close. Maintaining a lively e-mail correspondence may often be as good as being there.

Interaction is the third essential in tending to a friendship. You've got to write, you've got to call, you've got to visit. Find the nearest Starbucks and take time to catch up. "The specific activity doesn't matter," says Oswald. "The important thing is to interact."