"He who believes is strong; he who doubts is weak. Strong convictions precede great actions."
- J. F. Clarke

"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."
- Lyndon B. Johnson

Some consider this the most persuasive closing argument ever -
scene/clip from the movie 'A Time to Kill'

https://www.youtube.com/watch?v=4lnRK8QpC14

"Let one who wants to move and convince others, first be convinced and moved themselves. If a person speaks with genuine earnestness the thoughts, the emotion and the actual condition of their own heart, others will listen because we all are knit together by the tie of sympathy."
- Thomas Carlyle 

Transfer of biases, prejudices, feelings?......

People are persuaded more by the depth of your conviction than by the height of your logic -- more by your own enthusiasm than any proof you can offer.
- Cavett Robert