All knowledge is theory, and our belief in theories depends on varying degrees of evidence, bias and influence. Evidence is objective, but we all have biases, and we’re all influenced by forces beyond ourselves. All three inform reason and contribute to belief.
The conventional theory of gravity, for example, consists of some very simple phenomenological observations backed by a great deal of evidence and experimental repeatability. The mainline theory of gravity is aimed at describing and predicting the phenomenon, while it abstains from conjecturing any explanations of its origin and operational mechanisms. So while the underlying nature of gravity is largely a mystery to us, we’re pretty much unified in believing it because of the preponderance of evidence for its existence and the conservative reach of the theory.
To believe in any theory lacking evidence is folly, since it could very well be wrong. Favoring a theory is one thing, but due to bias and influence, most people will lay all their trust in theories without direct evidence. For two examples, consider the “big bang” theory and the theory of Darwinian macroevolution. Both theories lack any evidence to support their extended reach. Evidence exists, but it’s ambiguous and supports the alternative explanations too, namely creationism. But if you come at these two theories with a bias against a sovereign creator, for one thing, and you’ve been influenced by a secular education, for another, you’ll probably believe in them.
I have an extremely strong bias toward trusting the Bible, and I’m overwhelmingly influenced by the Holy Spirit. I also have very strong evidence bolstering my beliefs, making it a triple play (Hebrews 11:1). Consequently, I believe in creationism and reject the “big bang” theory and Darwinist macroevolution.
Like I said at the start, we all have biases and we’re all influenced by forces beyond ourselves. What are your biases? Who are your influences? Who do you trust, and why?