With a straight face, a person will say: "Who are you to say what truth is? What is true for you may not be true for me."
You can see how such a confused mindset would undermine evangelism.
The Bible teaches that Jesus is "the Way, the Truth, and the Life" and that there is no way to the Father except through Jesus Christ. Be very careful to note that it doesn't say that this proposition is true for some people and not for others or that it is only true for those who want to believe it.
That statement is either absolutely true in reality or not, but its truth does not depend on whether we believe it or we don't believe it.
But there can be no question that this kind of fuzzy thinking presents enormous hurdles for the evangelist who is seeking to spread the good news.
If he is approaching someone who doesn't even accept the idea of truth, it is obviously going to be more difficult to convince that person of the gravity of the matters under discussion.
In short, this type of postmodern thinking has led to intellectual and moral chaos that has undermined our society and our efforts to communicate the Gospel's message. —David Limbaugh (from, Beware of the Perfect Storm)