Most of our best-sellers are predictable titles — “Tropic of Cancer,” “Big Sur,” “Big Sur and the Oranges of Hieronymus Bosch,” etc.

But one title in particular title flies off the shelves for no obvious reason.

The book is Norman Mailer’s “The Executioner’s Song,” the riveting 1979 tome about the notorious killer Garry Gilmore.

Why do we sell so many copies of this massive doorstop of a book?

There are two answers and they complement each other as if part of a larger continuum.

The first is that when Magnus is working the front desk at the Library and people ask, “What do you recommend?” he invariably says, “The Executioner’s Song” (and/or “The Master and Margarita.”)

That alone is enough to ensure brisk sales. Who’d refuse a recommendation from Magnus? (He’s European, after all.)

However, there are instances in which the visitor approaches the book, feels its heft, considers its gnarly narrative, and becomes skittish. Then Magnus pounces. “Read the foreword by Dave Eggers,” he says.

The visitors read the introduction and are immediately floored by Eggers’ hyperbolic praise.

This usually seals the deal. Who’d refuse a recommendation from Magnus and Eggers?

For what it’s worth, I — frequently referred to as an “unnamed Library staffer” — took Magnus’ recommendation and tore through the book it in 10 days. It consumed my life. It was astonishing.

So there’s a third reason to read it: another glowing review, this time from an unnamed Library staffer.

And who’d refuse a recommendation from Magnus, Eggers, and an unnamed Library staffer?