My memory is flawed

I’ve had a copy of Lucifer’s Hammer, by Larry Niven and Jerry Pournelle, on my bookshelf since 1980. I know I read it. I could swear I read it. Yet, as I listed to it on Audible these past few days, I did not recognize a single line of the story. Nothing! I had a narrative in my head that did not match the book. How does that happen? I’ve referenced it dozens of times in conversation over the years. Heck, I even remember meeting Larry Niven back in the day. It's all gone. I remember nothing. The book is good though. I throughly enjoyed it. It's a great post apocalyptic read.