Have you ever opened up a brand new book and heard a crack? That is the sound of the spine breaking, which compromises the structural integrity of the book. The eventual result will be that the pages will separate from the cover, and the book that you just paid $24.95 for will unexpectedly collapse on you when you are reading in the bathtub.
Here is how to prevent that from happening, a timeworn technique shown to me by a little old librarian at Tarkio Elementary School:
1. You start with an unopened new book (it works for both hardback and paperback).
2. Holding the book closed with the left hand, place it spine down on a table or other hard surface.
3. With your right hand, take hold of the back cover and open it down to the table. Lean the pages to the left at about a 45° angle, then, exerting gentle pressure, run the flat of your fingers along where the back cover joins the book, from top to bottom and back, three or four times. Then do the same thing to the front cover (tilting the rest of the pages to the right).
4. Next, five to ten pages at a time (alternating sides), repeat that same process with the pages, smoothing with light pressure along the join of the spine while tilting the rest of the pages in the other direction. When you get to the middle few pages, part them in the center and gently crease the book flat. It is now flexible and fit for many years of undamaged reading.
The whole process only takes about two minutes, and is well worth it. And NEVER put an open book face-down to save your page. That can break the spine even if it has been conditioned. It is always better to use a bookmark.