"When two partners always agree, one of them is not necessary."
"If there is some point you haven’t thought about, be thankful if it is brought to your attention. Perhaps this disagreement is your opportunity to be corrected before you make a serious mistake." 
Disagreements will happen. Arguments will occur. Things might get difficult. And that’s a good thing. Get your facts, do your homework. Keep it as objective as possible. Don’t take it personally. If it’s about perspectives, let the other one talk first. Listen. Shut up. Listen some more. Then express your point of view.
Learning how to disagree is one of the best things that can ever happen to a partnership. And to a company. And to your life.
 Carnegie, Dale. How To Win Friends and Influence People. Simon & Schuster.