"It used to be slow. Cars, horses, and mail are slow. A lifetime is only enough to love one person." This lyric takes me back to my high school days. At our time, if you had a long-distance relationship, then you would know that dating is by special database writing letters. Writing a letter has transaction costs. Remember how much it cost to send a letter if you were both in the same city? It's 8 cents. Therefore, a letter sent in the past, and then sent back, have to spend 1 yuan. What if it was overseas? Sending a letter abroad is 1 yuan 2, and a round trip is 2 yuan 4. Therefore, my girlfriend's classmates in other places cried with tears, "It's too difficult for me." Because of the high cost, writing letters has become a luxury. But special database my girlfriend's friends abroad were unhappy when they heard it, "You are still shouting hard, I am too hard!" At that time, it cost 6 yuan to send a letter to the United States, and it was 12 yuan to send a letter back and forth. How many days does it take to save money to write a letter? But have you ever thought that because of the high transaction cost and long delivery time, it will lead to a problem- reduced transaction frequency. Because it is too expensive, I can only write a few less. So what does this lead to? Emotions are difficult to special database maintain. So, in order to keep the relationship, you need to inject a lot of affection into your letter. Then this letter must be very long, full of love and love.