This is a tough question to boil down. It’s more of a fine detail vs. broad strokes kind of thing.
Character reliability is so freaking important to the enjoyment of a book. As a reader, I have to be able to get lost in the world created with words. Be able to imagine myself in the story. For this reason, I’ve discovered I don’t read a lot of new (2000 or later-ish) young adult. I can’t really get lost in it all. However, stories of young adults set before that but not prior to the 70s, I can, depending on the writing. Young adults now who are so far removed from my age don’t even talk like I do or did. Their words and phrases are lost on me. I’ve said things to my kids that shocked them. Not because they didn’t understand it, but the meaning had changed from my generation to theirs. This causes me issues when trying to lose myself in a story where the characters are doing and saying things that are either lost on me or mean something totally different than the author intended making the scene sometimes nonsensical to me.
When I tell people this, they usually bring up the zombies and aliens I love so much. Asking how can I relate to that but not a 21 y/o living in modern New York. To me it’s simple, zombies and aliens can be, say, or do anything. The author establishes the world and creates clear rules, I can abide by them if they are implied or spelled out. However, there are real-world references for modern New York young adults that I cannot understand. Does that make sense to you? It does to me.
However, I can relate to other characters I have no experience as, such as someone with special needs trying to find love or a homeless single parent hoping to change their stars. While I am not those things, somehow those are examples of reliability lines I can cross.
I am unsure how to define that line for me or to point to it ahead of time and say, there it is, but I know it when I reach it between the covers.
Is this something you can relate to? If so, where is your line, can you define it? Do you know why it exists for you? I am super curious about this for others because I am puzzled by it many times myself.