When talking to non-Christian people, I often hear this question. They assume that what's true for me isn't true for them and visa-versa. What they call "truth" is mere experience.
For example, vacationers to the same location could hold different opinions. One could say it was lousy while the other could rave about how wonderful the place was.
Truth is true for all people. We know that light travels at the same speed throughout the universe. Gravity operates the same way too. All main sequence stars burn using the nuclear fusion of hydrogen into helium. Truth is what is, not what we experience.
An excellent Bible scholar named Ravi Zacharias told a story about an argument he had with a man who doubted that truth was true for all people. Ravi finally got through to him that we all avoid being run over by cars in whichever land we live. Therefore, a person's philosophy won't protect them from a collision.
Much of the "your truth - my truth" argument is mere wishful thinking. People don't want to admit that they're born wicked. Nobody, including me, wants to honestly face their evil acts and impulses. This is why human beings fight so hard against Christianity.
My next book called You Think You're Going to Heaven? will delve much deeper into this matter than I can on my blog. I've only written a few pages but I hope to finish the work by the end of the year. Like announcers say on the radio, "Stay tuned."