Although I’ve never heard this explanation, I am convinced that this, like taking of your shoes, is based on an almost lost superstition rather than any practical or social factors. In Korea, anything that someone has written their name on has to be treated with the same care as a business card in Japan. I caused a scandal by writing an error correction on the back of a piece of paper that someone not in the class on that day had used as a name tag the week before.
Why do you have to be so careful with business cards?
December 27, 2008 at 10:37 pm (Japan and Korea, Japanese business and economics, Japanese etiquette and manners, Japanese religion and superstition)
Japan Explained FASAQ 
Catie said,
November 13, 2010 at 10:14 pm
The business card represents the person, so if you put in in your back pocket and sit on it, you are sitting on the person. You have to treat the card with as much respect as possible. Get a card holder, that is really the only respectful place to put a card. Then put it in a breast pocket or purse.