It was written by the author whose name was uncertain. We can learn from the biography his famous students: Yi Zhang and Qin Su,were very impressive persons during the era of Chunqiu and Zhanguo .There are so much uncertain things about GuiGuZi, which made the author and the book amzing.
It was considered the First book about psychological,debate and war, which taught people how to know the thoughts of others, how to make others happy or sad, how to konw the truth or the lie, how to attack and defend.
The era of Chunqiu and Zhanguo is complex period. We China was devided into senven main countries, and Qin is the biggest and strongest one, which was at the west of China. Qin tried their best to make all the countries to become unity one, other countries wanted to keep them indepentent and free, at last, war was inevitable. there were senven kinds of forces,which made the war complex. One country are hostile with another one today, and maybe they become friends for common benefits tomorrow.
The complex background made the GuiGuZi become a powful book, espeacily with the success of YiZhang and QinSu, They were soldiers without hands, but with the mouth and brain, which are more powful than hands, and they opend an era: you can kill people with your mouth; you can change others' decison by debate quickly; it is popular to pursuit wisdom, and so on.
Undoubtily, it was a amzing time. Maybe you can learn something from the histroy and GuiGuZi. Enjoy it!