A large Chinese character, Double Happiness, on a red piece of paper or in paper cut is always put where it must strike the eyes on a young couple's wedding. It has a story behind it.
In the ancient Tang Dynasty, there was a student who was on the way to the capital to attend the national final examination, in which the top learners would be selected as the ministers in the court. Unfortunately, he fell ill halfway when he passed through a mountain village. Thanks to a herbalist doctor and his daughter, he was taken to their house and treated well. He recovered quickly due to the father and the daughter's good care. Well, when he had to leave, he found it hard to say good-bye to the pretty girl, and so did she. They fell in love. So the girl wrote down the right hand part of an antithetical couplet for the student to match:
"Green trees against the sky in the spring rain while the sky set off the spring trees in the obscuration."
"Well, I can make it though it is not easy. But you'll have to wait till I have finished the examination." replied the student. The young girl nodded in significance.
In the examination the young man won the first place, who was appreciated by the emperor. Also the winners were interviewed and tested by the emperor. As luck would have it, he was asked by the emperor to finish a couplet, which would need a right part as the answer. The emperor wrote:
"Red flowers dot the land in the breeze's chase while the land colored up in red after the kiss."
The young man realized immediately the right part of the couplet by the girl was the perfect fit to the emperor's couplet, so he took the girl's part as the answer without hesitation. The emperor was delighted to see the matching half of his couplet was so talent and harmonious that he authorized the young man's identity as Minister in the court and allowed him to pay a visit to his hometown first before holding the post. The young man met the girl happily at home and told her the emperor's couplet. They soon got married. For the wedding, the couple DOUBLED the Chinese character, HAPPY, together, on a red piece of paper and put it on the wall to express the happiness for the two events. And from then on, it has been taken on and became a social custom.