Nobody knowingly joins a cult, so why are so many lives ruined by them?

Sarah Steel's new book, Do As I Say, dives deep into the motivations of people who join cults — and the tactics used to lure them in.  (Supplied)

"Nobody joins a cult" is not a statement you’d expect to hear from someone who has spent the last few years investigating how widespread they are.

But at second glance, it goes to the heart of what Sarah Steel has repeatedly found as she traverses a secretive and bizarre world for her hit podcast Let's Talk About Sects.