As Eliezer said in Searching for Bayes-Structure:

The way you begin to grasp the Quest for the Holy Bayes is that you learn about cognitive phenomenon XYZ, which seems really useful - and there's this bunch of philosophers who've been arguing about its true nature for centuries, and they are still arguing - and there's a bunch of AI scientists trying to make a computer do it, but they can't agree on the philosophy either -

And - Huh, that's odd! - this cognitive phenomenon didn't look anything like Bayesian on the surface, but there's this non-obvious underlying structure that has a Bayesian interpretation - but wait, there's still some useful work getting done that can't be explained in Bayesian terms - no wait, that's Bayesian too - OH MY GOD this completely different cognitive process, that also didn't look Bayesian on the surface, ALSO HAS BAYESIAN STRUCTURE - hold on, are these non-Bayesian parts even doing anything?

• Yes: Wow, those are Bayesian too!
• No: Dear heavens, what a stupid design. I could eat a bucket of amino acids and puke a better brain architecture than that.