In a new book, “The Sibling Effect,” Time Magazine’s senior science writer (and one of four brothers) Jeffrey Kluger digs deeply into the impact siblings have on each other’s lives … and there are some tidbits for parents too, like this one:

“One message I have for parents is that they should quit feeling guilty about having a favorite,” he writes. “I like to say that 99 percent of all parents do have a favorite child and the other 1 percent are lying through their teeth.”

He adds that being a favorite won’t necessarily serve a child well in life anyway: They may be unprepared for criticism in the real world.

Read more about ”The Sibling Effect” and raising siblings here, from the ABC News Health page.