Philip Roth once wrote "Truth is stranger than fiction, but stranger still are lies." And he is right.
We see today that world leaders can transparently and provably lie and yet their statements are treated as if they are newsworthy.
Diplomacy is based on the assumption that both parties are trustworthy. But for some reason, even when one party is proven to have lied over and over again, in today's world people are willing to give them more and more chances - as long as they aren't the ones who can be directly affected by the lies.
Even bald-faced lies can have the effect of buying time, of causing the listener to pause and reconsider. People want to believe so much that they will allow themselves to believe the words of known liars.
So lies almost always work, on some level. And as long as they are rewarded, they will be repeated.