Character drives story. I cannot read a story about a character that is inherently uninteresting; by that I mean unrelatable. In order for a character to be interesting I believe the reader must be able to relate to them in some fashion. Relating to someone doesn’t mean that we share things in common–not in the traditional sense. If I read a book about a school shooter or a serial killer I would not do so because I have the same desires within me. I would do so because I have been exposed to the same conditions in some way that they have. I have been in a position where I went to high school and grew angry at people or I lived in the same locale as the killer and dealt with that world. it could also be that I recognize those conditions and have some basic curiosity about the effects of such things on a psyche. I.e. the question: How do you survive and what would I do? A good example of this is Derf Beckderf’s My Friend Dahmer, which chronicles his uprbringing alongside Jeffery Dahmer. The story made Dahmer relatable, because Dahmer wasn’t raised to be a serial killer and Beckderf never knew he would become one, though through the reading you can see that the signs were there. I identified with Beckderf, because he was in a situation where he was exposed to all kinds of weirdness. Likewise, I identified with a lot of what Dahmer was exposed to as a kid.
What it comes down to for me as a reader is different responses to similar stimuli. How your character reacts to things is what makes them unique. It also can make them relatable if you write the story in a way that shows how their makeup creates the reactions. That therefore triggers us to wonder how our own makeup would determine our reactions.