Understanding is essential to agreement. Both parties must have access to true and relevant knowledge. If I am not sure that what you say is true, I cannot agree, unless I intend to lie. Our generation has learned the art of manipulating media, deliberately distorting truth, circulating utter lies as facts for the purposes of ideological or political advantage. No wonder ours is also a cynical generation.
People are hard-put to believe in anything.
On top of this, we have the added problems of language barriers, communication failures and ignorance. But there is no way around it. Despite these obstacles, if we cannot agree on some basic things to be both true and valuable for our world, we will have no long-term peace, unity, harmony or lasting happiness. Knowledge is not enough. We must also be willing to do that which we honestly see as the best and wisest choice, or our education will only make us more informed hypocrites.