Characters. Every great novel or work of writing needs them. Without good characters things fall flat regardless of how well something is written.
But, how do you know readers will find your characters interesting enough to keep on reading?
1.You find yourself yelling "there's no way he/she would do that."
You know them so well.
2.When you're writing a scene you find yourself getting into their head space and hearing, smelling and feeling what they do.
You're not there with them - you are them. At least whilst you're writing the scene. We're not talking multiple personality disorder here, but it might feel like it.
3.You find yourself talking about them in every day conversation as if they're a friend of yours or even a family member.
4.You start placing them in your favourite novels and TV shows relishing how they would react if they met your favourites in that book or TV show.
5.You can place them in any scene and you know how they will react. You don't have to overthink it.