The quickest way to turn a friend into an acquaintance is to send him a card once a year, for one occasion or another.
Let me qualify—right off the bat—that I am not talking about a situation in which you maintain an ongoing and active friendship with someone, and the card sending is part of it. In that case, sending a card is a very nice thing to do, indeed. I am talking about a situation in which sending a card, on very rare and predictable occasion, is all you do. Don’t be surprised if your friendship with that person died long ago. Friendships require maintenance—just like everything else. If you can’t pick up the phone, go visit, or generally stay involved in a person’s life, perhaps it is best to admit that you have grown apart and no longer share the closeness you once did. To be sure, not sending a card to an old friend might sting for a minute, but I am going to guess the other person will get over it, quickly. They might not even notice you stopped sending cards. Sad to say, but true.