1. No legal rights basis: For example, Kun lacks legal rights basis related to the defendant, such as intellectual property rights, trademark rights and reputation rights. Then he can't successfully send a lawyer's letter.

2. Insufficient evidence support: A lawyer's letter usually needs to provide sufficient evidence support to prove the defendant's infringement or other illegal acts. If Kun lacks sufficient evidence to support it, then he can't successfully send a lawyer's letter.

3. There is no lawyer's letter that conforms to legal procedures: the lawyer's letter needs to conform to legal procedures and regulations. If Kun fails to comply with relevant legal procedures and regulations, the lawyer's letter will be considered invalid.