You need three things to become a successful novelist: talent, luck and discipline. Discipline is the one element of those three things that you can control, and so that is the one that you have to focus on controlling, and you just have to hope and trust in the other two.
All writing is discipline, but screenwriting is a drill sergeant.
His father, that austere, unfeeling and untutored man, had insisted his sons polish their boots every evening. Flett has learned to be grateful for this early discipline. It kept him breathing as a boy, provided a pulse, gave order to vast incomprehension. Later he found other ways.