When a Business Insider writer heard about Dr Michael Breus’ new book, “The Power of When,” in which he helps readers figure out their biological predisposition to be a morning person, evening person, or somewhere in between, and then figure out their ideal daily routine based on that predisposition, she was intrigued.

Breus is a clinical psychologist and sleep expert; he calls himself the “sleep doctor.” When we spoke by phone in July — Breus has a practice in Los Angeles — he told me that he first started researching this topic when he noticed that his treatments for insomnia weren’t working on a select group of his patients.

“What I realized,” he said, “is that my patients didn’t have insomnia — it turns out they were night owls. At least some of them, anyway.”