The tip didn’t sink the Titanic. It was the iceberg under the Atlantic that gets props for that.
Character creation is no different. The reader only sees the tip, but you must know your character backwards and forward.
The moment you begin to imagine character relationships - how your character deals with his parents, his siblings, his coworkers, and all that - you start to explore the world of your story. As you develop backstory and establish personality, you start putting the character in different situations in your mind, and you begin to imagine him or her in the most mundane and most exciting moments.
The courage to deal with the trivial and banalities is essential. Because often the best stories are made from the most commonplace material, and if you don’t know how your character cooks dinner, does laundry, brushes his teeth, or what her little vexations are, her petty likes and dislikes, a dynamic, a full story will never happen.
A great way to begin filling in the entire iceberg is to ask questions. Using a character questionnaire will open you up to new ideas, situations, and relationships. Knowledge is power. The more you know about your character, the better your script will be.