How about something like this?
The world was here before you were. Therefore you didn`t make the world. Each and every thing in the world exists according to innate logic, such as dogs making dogs, and cats making cats, and cats behaving in cat-like ways, each according to their own innate logic. Simple observation proves the existance of this logic, and logic cannot exist without intent, as the absence of logic is chaos, and chaos never leads to cohesion, but only to destruction. Because life operates according to pre-established rules, it is up to us to correctly interpret reality, not to invent reality.
I`m not at all sure if this helps or not. It sounds like you`re talking about atheists. In those situations people are erroneously using the word truth as a stand-in for opinion. We can make our own opinions, but we can`t make our own truth. Truth is independant from opinions. If you`re talking about Christians, the explanation is much easier: just remind them of scripture.
In the beginning God created the heaven and the earth.
-Genesis 1
and
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
-John 14:6
I hope I`m not getting in over my head quoting Scripture here like this.