Years ago, I took a communications course from a professor who announced on the first day, “There’s no such thing as altruism.” A staunch proponent of exchange theory, he insisted that all social interactions are governed by people’s desire to gain a reward in exchange for providing something of value to others.

I gamely attempted to argue with him. Surely, there are genuinely selfless folks and acts of altruistic behavior.  “Look at Mother Theresa,” I ventured. “She devoted her life to serving the poor and expected nothing in return.”

He quickly pointed out that she derived substantive rewards from her generous acts of service—the psychic satisfaction of feeling that she was a person aspiring to do good while doing God’s will, as well as the appreciation of others.

I still don’t think Mother Theresa sat around calculating, “Let’s see. If I devote my life to serving the poor, what’s in it for me?” But I do think this provocative professor had a point. Psychic rewards count too.

I was reminded of this the other day. I have a dear friend I go to lunch with once a week. Still writing beautifully at 94, she’s one of my role models—and great company to boot. Sadly, her body hasn’t held up nearly as well as her sharp mind. When she confided that she really missed going to Barnes and Noble, I volunteered to be her chauffeur. I threw the wheel chair into the trunk of my car, and off we went.

The moment we entered the store, my friend looked as if she’d arrived at the Promised Land. She eagerly pored over the books displayed on tables of “must-read” fiction and new releases. She selected several, along with a batch of greeting cards and an engagement calendar.

On the drive home, my friend’s eyes shone as we talked about how much we loved books and bookstores. She thanked me over and over for taking her, and the next day sent me a lovely email declaring it had been like having a second birthday.

You can guess how I felt—like I was the one who’d received a terrific gift.

So, I guess I’d have to agree with my professor. Life does involve a myriad of exchanges. The most delightful kind occurs when we haven’t even counted on receiving anything in return.