Cao Cao suffered from headache and dizziness for some time. He did not respond to any treatment.
Finally he was cured by Hua Tuo with acupuncture. So Cao Cao would like Hua Tuo to stay with him as his family physician. But Hua Tuo refused the invitation with some excuses.
Cao Cao was so angry. He decided to kill Hua Tuo.