If you constantly surround yourself with people that only agree with you, you are destroying your opportunity to gain perspective. Perspective, is possibly one of the most valuable things we must acquire in order to learn to react to situations accordingly.
Unlike other people who talk about this subject, I like to emphasize on the fact that gaining that perspective is uncomfortable. Befriending or simply talking with people that disagree with you is something no one can really do without feeling conflicted.
If you've sat there and said to yourself that there is no need to talk to someone, because you know you are right, more often than not you've chosen wrong. Basically, a conversation, a discussion is nothing more than an attempt to gain perspective on a situation that people can't agree on.
Imagine anyone saying to you in a serious tone of voice. "I know everything, no need for me to learn more". You would think, and you would be correct that your friend has gone quite mad and has possibly become quite ignorant of how life works.
My message I guess is that, be uncomfortable sometimes, engage in dialogue, talk to those who see the world from a different lens. Be respectful, there is no need not to be, but I can guarantee that if you are open minded, and if you are willing to bare with the discomfort, you will walk away a little wiser.
@hasanulbasri