This is a judgment sentence, and the meaning can be understood in reverse. The best persuasion is excellent demonstration. As the saying goes: mule or horse, pull it out for a walk. Have the same effect.

Trying to convince others is not something that everyone can do and do well. Say it again and you won't have to listen. What a person says is the most convincing, and that is personal practice. . . . . .

Sorry, I'm in some trouble. I can't write any more.