I'm sure, like me, you have seen many different movies, television programs, and read many, many books. I don't remember all the things that happen. I might have scenes that stand out in my memory bank, but mostly it's the characters I remember.
For instance, I loved the series of "Who's the Boss?" I can't tell you much about the silly episodes, but I remember the chemistry between Tony and Angela. Their characters are still vivid in my mind. My current favorite series is "Castle." I don't watch for the murder they solve or how they do it, but for the characters of Rick Castle and Kate Beckett. I loved Gone With The Wind, but I don't remember many scenes...just a few major ones and what keeps them fresh in my mind are the characters, Scarlet and Rhett. Without great characters, it is easy to forget.
Authors must be cognizant of making their characters come to life on a page. They must have individual voices, personalities, baggage, and charisma. We learned as toddlers to remember things by "seeing" them. A chair, a table, a nose, a smile, a dog, a cat...and the list goes on. Likewise, we remember great books by seeing the characters and the action playing out in our brain. It takes a good writer to be able to paint those pictures for the reader.
Do you have characters you remember vividly?