The Japanese Concept of Being Fortunate
Just as the number 13 is bad luck in the United States and many other Western cultures, the Japanese have similar auspicious and inauspicious numbers. The Japanese consider the numbers three, five, and seven to be very lucky. They even hold a special celebration for children who are turning any of these three ages within a given year. It is called 'Shichi, Go, San' (7, 5, 3) and is held in the honor of children.
The Japanese however, consider several numbers to be bad luck. The worst are four and nine. Four is pronounced 'shi' which is also the word for death. Nine is pronounced 'ku,' the same as the word for suffering. Forty-two is also very bad, pronounced 'shi-ni' because it means 'about to die.' Forty-three, or 'shisan' can be said the same way as the word for stillbirth. Obviously when possible you would want to avoid these numbers.
There are actions which are also bad luck to the Japanese. Sleeping with your head to the North should never be done as this is the way the dead are laid in Buddhist tradition. Any other direction should be fine. Also, you should never stand your chopsticks up in your food. This image is similar to what it looks like when incense sticks are placed in a Buddhist altar.
The Japanese are superstitious in general, with many of these ideas stemming from their Buddhist and Shinto beliefs. Many people in Japan believe it is bad luck to kill a spider in your house as it is a soul being given a second chance to climb out of hell in the form of a spider. Those who are eternally condemned are not given this second chance. If you kill the spider you can take on its bad fortune.
Most Japanese carry or have an omamori good luck charm. This is a small, rectangular protection charm that you can get from Shinto temples. They are blessed there and can be used for anything from travel safety to good luck in school. Another symbol of good luck is the turtle.
Finally, other religious beliefs have their share of influence, too. In old Japan, there were a group of seven gods called the Shichifuku Jin or Seven Lucky Gods. They had a range of powers. The female goddess was the goddess of knowledge, while others dominated long life. You would pray to the one that suits your needs at the moment. Just as they had the power to bestow good luck on you, they could also bestow the bad.
It is a good idea to find out a people's idea of luck before visiting any country. This way you can avoid cultural taboos before committing them and have fun participating more in the culture.