What does it mean that a mouse falls into a rice jar to tell fortune?

The mouse fell into the rice jar to tell fortune.

Happiness depends on misfortune. It seems to be a blessing, but it is actually a curse. As the saying goes, don't pursue too much in everything, just pour eight points of tea, leave three points for others to talk about, don't be too full, and leave yourself a way out. Don't be greedy when you are alive, or you will only suffer the consequences. This is the central idea. It revolves around writing.