That's reputed to be an old saying in the movie industry.
In What Happens at Christmas, I did both.
I have no idea where Misty - the heroine's four year old niece - and Griff, her very independent minded cat, came from, but they were an essential part of the story. And as soon as I knew there was going to be a cat, my thoughts immediately turned to Ming. And he became a kind of pattern for Griff - not in personality, because Ming was a much gentler cat that Griff is - but the fact that he had a big enough spirit to become a family legend.
Most of Ming was white chinchilla, but he had a patch over one eye that was ginger and so was his tail. My Mum said it looked as if it had been stuck on. I can only go by what my Mum said, and a few old and blurry photos, because Ming actually died before I was born.
But he was remembered. And that takes a cat with personality, which is what I wanted for Griff. There were all sorts of family tales about Ming. He arrived home as a tiny kitten in my aunt's handbag - one of a litter from a girl she worked with. He was covered in lipstick and reeking of scent, as all the girls in the beauty salon had kissed him! My Mum named him, as naming of family cats was apparently her job, and as London Zoo had just acquired a new panda, called Ming, that was what he became. (Although apparently the original panda was a she, who has recently been immortalised as a statue at the Zoo. )
And then there is the family legend - Ming was a very loving cat, who would meet my mother and my aunt at the bottom of the street on the way home from work and follow them home, jumping from wall to wall, and he wasn't supposed to sleep on the chairs, but my grandmother always knew, because of the white hairs and ...
Well there are countless stories, and I wanted to create that sort of cat. I hope I have, with Griff.
And that's why one of the dedications in the book is to commemorate Ming. I think he deserves it.