When I was in college (multiple lifetimes ago) I took a class where we studied the nature of belief and disbelief. It was actually a class about logic and situational analysis, but (despite being raised Lutheran) I attended a Jesuit college, so the emphasis on belief versus disbelief was well aligned with their gestalt.
I loved the class (for many reasons, not all of them scholastic). The topic of what we believe — or disbelieve — has fascinated me ever since. It’s a key branch of philosophy under the umbrella of epistemology, the theory of knowledge.
Because our beliefs affect everything from science to politics to personal relations.