8. You lose your cool
This can sabotage your chances for getting what you want even if he agrees with you. If you get angry or annoyed because he's not giving you what you want, you need to take deep breaths to calm yourself down. Anger will only beget more anger.
Any chance of persuading him to agree with you is lost if you get upset. He will see only that, and emotion will replace his logic. Promise yourself ahead of time to keep your voice level, no matter what.