Critics have been condemning George R.R. Martin for missing his deadline on The Winds of Winter, the next novel in the Song of Ice and Fire series, which is the basis for HBO's Game of Thrones show. They say that he needs more discipline.
It takes more than discipline. It also takes opportunity, experiences, inspiration, and many other factors. Authors have lives, too. They have tragedies and triumphs, doctor's appointments, family matters, and everything everyone else has to deal with. If they do nothing but sit and write, they won't have those experiences to inspire them and write about, and their work would be nothing but fan fiction. If they write to a deadline, their work would be rushed and shortcutted, and lower quality. If they write for profit, their work would be formulaic and pandering, and the reader would not profit. Many authors do make compromises, working for hire instead of higher work, and it shows. If you're satisfied with compromised work, then that's what you can expect when you put limits on an author. Forgive the limits, and you may be disappointed by the wait, but you won't be disappointed by what you finally get.