Why do we celebrate the Moon Festival?
Here is Wickipedia’s answer:
In the ancient past, there was a hero named [Hou] Yi who was excellent at shooting. His wife was Chang’e. One year, the ten suns rose in the sky together, causing great disaster to people. Yi shot down nine of the suns and left only one to provide light. An immortal admired Yi and sent him the elixir of immortality. Yi did not want to leave Chang’e and be immortal without her, so he let Chang’e keep the elixir. But Feng Meng, one of his apprentices, knew this secret. So, on the fifteenth of August in the lunar calendar, when Yi went hunting, Feng Meng broke into Yi’s house and forced Chang’e to give the elixir to him. Chang’e refused to do so. Instead, she swallowed it and flew into the sky. Since she loved her husband very much and hoped to live nearby, she chose the moon for her residence. When Yi came back and learned what had happened, he felt so sad that he displayed the fruits and cakes Chang’e liked in the yard and gave sacrifices to his wife. People soon learned about these activities, and since they also were sympathetic to Chang’e they participated in these sacrifices with Yi.