SNARKY RESPONSE: I wish someone had told Mr. Porter that back in high school. He was King of Historical Trivia and we lived in fear of forgetting to detail every little tidbit that tripped off his tongue.
A good memory is one trained to forget the trivial.
But in writing, as they say, the Devil's in the details.
Nothing will yank a reader out of your story any faster than for you to make a mistake with a character's name. Or have your character leave the room and then never come back even while they carry on a conversation with another character in said room. Or have their Uncle Frank sudden undergo a unmentioned sex change to become their Aunt Frankie (unless it's part of the story).
To be fair, when writing a novel, it can become a little hard to hold all that stuff in your head. One device for this (actually borrowed I believe from screenwriters) is a Writer's Bible. I admit I've never actually used one, but I'm beginning to see the benefit.
As I understand it, the Writer's Bible is where I would shove all those details that can be lost as I follow my characters down the rabbit hole. Character sheets to keep track of little things like hair color, accent, relationships, favorite ice cream flavor. Location descriptions to keep track of how run down the bar is, does the seafood restaurant look like a schooner or a pineapple. Genealogies so I remember there actually IS an Uncle Frank who likes to cross dress. Maps so when my characters walk two blocks to the bar in Chapter 1 it's not suddenly in the next county in Chapter 10. Chronologies or timelines to help keep track of events outside of my main storyline. Plot points to keep me on track.
What other things would you keep in your Writer's Bible?