A visible illustration is gravity. In my world I can believe that gravity does not exist, but if I were to test this by jumping out of a window, I might soon become a convert realized that gravity is indeed an absolute reality on this earth. Indeed, different people find different answers to life and death, but since these concern physical realities, some, if not all of us have to be wrong because of contradicting beliefs. The reason why I am so convinced that the God of the Bible is an absolute reality is because I've tested His words over and over again and have found no fault or contradiction. The Bible makes thousands of claims that are testable.
Slavery is another example.
It can be very dangerous to believe something that is untrue because it is comfortable and because it fits with what we desire. I would much rather shake up my world view by discovering the truth than remain deceived by a comfortable lie. This is why I constantly test the claims of the Bible, because if I am being deceived I want to know.