What convinces is conviction. Believe in the argument you're advancing. If you don't you're as good as dead. The other person will sense that something isn't there, and no chain of reasoning, no matter how logical or elegant or brilliant, will win your case for you.
What we won when all of our people united must not be lost in suspicion and distrust and selfishness and politics. Accordingly, I shall not seek, and I will not accept, the nomination of my party for another term as president.
When things haven't gone well for you, call in a secretary or a staff man and chew him out. You will sleep better and they will appreciate the attention.
You do not examine legislation in the light of the benefits it will convey if properly administered, but in the light of the wrongs it would do and the harms it would cause if improperly administered.