It is by universal misunderstanding that all agree.(C'est par le malentendu universel que tout le monde s'accorde.) – Baudelaire
We might be inclined to agree with Baudelaire. In many situations, people caught up in the enthusiasm of a crowd or hypnotized by the rhetoric of a ceremony claim to be in agreement with one another -- and, they often fervently believe it to be so.
The bride and groom at a wedding ceremony may agree to "love, honor and obey." But question them privately afterwards and you will find discrepancies between what each of them explains is their understandings of those words. If no discrepancies initially turn up, ask them after the honeymoon is over.
However, what Baudelaire seems to overlook is that an agreement is often little more than an expression of concession or acquiescence. Faced with a potential impasse, parties may make concessions or acquiesce in a formulation of mutual responsibilities that none really find optimal.
Why would they do such a thing? Because, by examining their options parties to a negotiation may find out that concession or acquiescence is less costly than disrupting relationships with their opponents by, say, walking away. You don’t sever relations with someone you might need to depend on in the future, even if, for the moment, you might strongly disagree with them. (See Choosing The Lesser Evil: a Moral Failure?)
Such realities keep unsatisfied voters from switching political party, bad marriages from divorce or antagonistic nations from war.
To examine these issues further, see The Indeterminacy of Consensus