Kindle devices are getting more and more popular with book lovers.With its lightweight material, readers no longer have to carry thick books wherever they go.

Also, the instant download features save them the trip to the bookstore, where they may be surprised by the long line for the cashier or a "sold out" sign. However, some people don't get it. Some people still believe printed books are better than digital ones.

"I just don't see the appeal," Bob Quarteroni writes in The Morning Call. "Especially when I see people trying to tilt their screens so they can read in bright sunlight or listen to someone moan about the price of downloads."

"What's the fascination?" he asks.

The answer, according to Business Insider, is secrecy.

In 2012, BBC reports that Amazon sold 114 e-books for every 100 prints of the same title. One of the strong factors that have affected the e-books sales is the increasing popularity of erotic novel "Fifty Shades of Grey."

While some teens may feel proud, even honored, to be seen reading "The Hunger Games" or "The Fault in Our Stars," some of them certainly do not want to be caught reading "Fifty Shades of Grey" in the school bus.

"Using an e-reader also allows you to avoid making unintentional statements with your literary choices," says Business Insider.

To let readers enjoy a more private reading experience, Amazon announced in a press release a new feature that lets users share quotes and recommendation only to specific people.

Before, Amazon allowed readers to quotes through Facebook and Twitter, where all their friends and followers can see what they're reading.

"Often when you are reading a book, a quote inspires you to think of someone," says Amazon. Some funny quotes are only meant for best friends while some romantic words are only meant for certain special people.

"The perfect quote in a book isn't always the perfect quote for your whole social network," said Kindle's senior vice president Russ Grandinetti in the press release. "Now it's easy to share exactly what you want in a Kindle book with exactly who you want."

"Kindle makes it easy to chat about the books you're reading, whether it's making a recommendation or sparking a conversation about a quote you loved. And friends who receive the share can instantly start reading a free sample of the book—no sign-up, no sign-in, and no app to install."

The same principle applies for people using Kindle for privacy. The perfect book to read may not be the best for others who can see the cover.