Eccentricities. Those odd things about you which make you, you.
I read a book entitled, Greg’s Microscope, an easy reader, when I was rather young. In the book, the main character, Greg, looked at slides with his microscope of salt, sugar, and pepper. Salt and sugar were crystals. Pepper looked like dirt. Why that little tidbit stuck with me, I don’t know. I do know that from that day on, I wouldn’t use black pepper.
In my twenties, when I really began to get into cooking, I eventually used white pepper, then later I used paprika. I still don’t use black pepper. (I do occasionally use cayenne, when I’m cooking a special dish for my husband, but I digress.)
When you create a character, maybe you saw someone doing something somewhere that made you think of a story, you have to add those odd little bits which make your character real. The contradictions which are human – growing up being taught one way, and deliberately going another is one example.
A dear friend of mine had stopped eating pasta with tomato sauce before we backpacked through Europe a few decades ago. Instead, she found her favorite dish in Italy – penne panne alla prosciutto – tubelike pasta with cream and ham.
For every trait your character has, you need to have a reason why your character does certain things, or doesn’t do certain things, for the character to be believable.
Think positive. Write on.