The whole sentence is "a horse is not worthy of two saddles, and a loyal minister does not serve two masters". ? Loyal ministers will never assist the monarchs of two dynasties; A virtuous woman will never marry a second husband, which is the ethics of feudal times. Metaphor is loyalty and faithfulness, and there is no second heart.
The details and the original text are as follows:
A collection of six words in A Collection of Celebrities
If you read the book of Confucius and Mencius, you will get the courtesy of the Duke of Zhou. A gentleman is respectful and courteous to others. It's a shame to count your friends, but it's a shame to count your friends. People can't pay heaven, and heaven has the heart to support people. A horse does not have two saddles, and a loyal minister does not serve two masters. Think of a powerful slave, not a son of inaction. People have fortunes, and now there are yin and yang day and night. A gentleman accumulates wealth in power, but a villain bullies others. People put ceremony and music first, and trees turn branches and leaves into circles. The horse has the meaning of hanging the reins, and the dog has the grace of wet grass. When gold is shipped, it will be eclipsed, and when it comes, iron will win glory. Don't do it if you are afraid of people knowing, but respect and study hard. Mount tai is not only slightly annoyed, but also makes a small base into a tall one. Humanity who has no troubles, wind and waves also grow old.
Seven Words in The Collection of Celebrities
Loyal ministers don't serve two kings, while heroic women don't marry two husbands.