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.
Despite the title, this post isn’t as strongly related to 
Logos con carne 