Sometimes you can say it with a card.

For years, even before his company was a huge name, Under Armour CEO Kevin Plank sent Nike co-founder Phil Knight a holiday card that said “you will know our name.”  He explains why in an interview with “Sunday TODAY” host Willie Geist, airing Sunday

He says that “it wasn’t spiteful,” and instead that he meant it, even though most people told him he wasn’t even on Nike’s radar. “To me, we were always on the radar. To me, were always in that game. To me, we’re always in that fight,” says Plank.

Whatever his reasons, there’s a lesson in this for us all: Holiday cards may matter to your career. In general, sending them is about “relationship building”, says Cheryl Lynch Simpson, a career and job search coach.

And that relationship may even be with a competitor: “I do think it’s a good idea to send holiday cards to competitors,” says Cheryl Palmer, the founder of Call to Career. “In the world in which we live, your competitor today could be a partner tomorrow. Or your company could merge with that competitor. All of this means that it makes sense to cultivate good relationships with competitors. Sending greeting cards is one way to do that.”

Sending cards to clients and potential clients is also savvy.  Executive coach Marc Dorio says cards to current clients help generate goodwill and to potential clients it’s a way to keep your name in view. “It’s a nice touch to receive a card in the mail from someone that you do business with,” says Palmer.

And “if you own a business, and you potentially want to do work for another business, it makes sense to reach out to that business, and sending a holiday card is one avenue of doing that,” says Palmer. “If you want another company to buy your company, sending a holiday card is a way to create goodwill.”

Of course, “sending holiday cards alone does not a good relationship make. There needs to be face to face and/or phone contact as well,” she adds. And “if you simply send the card blindly, it may not achieve its objective because it could easily be thrown into the trash without the name of a recipient.”