There are many traditions and legends during the Chinese New Year, and one of most important ones is about why Chinese New Year is celebrated.
It is said that long time ago, there was a monster called Nian (年), and he lived under the ocean. However, at the end of each lunar year, he came out from the water and went to the village to eat livestock and children.
To avoid being hurt by Monster Nian (年), people would run in the mountains and hidden there till next morning.
One year, when people were packing their belongs to leave for the mountain, a sage came to the village and told people that he knew how to drive away Monster Nian (年) if he can stay in the village for the night.
People did not believe him because they knew Monster Nian (年) was very ferocious and urged him to hide in the mountain together. However, the sage insisted and stayed in the village. Realizing they cannot convince him, people escaped to the mountains.
Monster Nian (年) came to the village as usual to look for livestock and children. However, he found the houses were full of light, also decorated with red papers. When he got closer to the houses, the sage lighted firecrackers. Monster Nian (年) was scared by the sound and light and run away.
Next morning, people returned and found the village was not destroyed as usual, and then realized the sage was a God coming to help them. They also found the weapons the sage used to drive away Monster Nian (年). Since then, door couplets, firecrackers and sitting up late with light on became traditions during the Chinese New Year.
Chinese New Year was locally called "guo nian (过年)", meaning to "fight and survive from Monster Nian (年)".