Need help in getting through the "dip"—where you feel like giving up? These five books on productivity and focus will help you get through the valleys when things get tough and you feel like quitting or starting over on something else.

Overaching themes covered in these books: things start out fun, but quickly get tough. This is when most people will quit. Seth Godin refers to this as being in "the dip" where effort and time no longer produce the same results. He argues that once you decide to commit, see it all the way through. Difficult things are hard to achieve and therefore create scarcity. Scare things are valuable.

Ryan Holiday's book "The Obstacle is the Way" reflects on the Stoics (Ancient Greek philosopher Marcus Aurelius' "Thoughts on Meditation"). It's a more philosophical approach on why you should learn to love difficult things. He argues that in failure are a complete set of instructions on how to succeed. It is only through failure and difficulty do we learn.

"The Compound Effect" written by Darren Hardy is the seminal classic about compounded interest. Small, smart choices, applied consistently over time can have dramatic results. Big things have humble beginnings. By doing the work everyday, you essentially commit yourself to making small, almost imperceptible progress towards your goal. He also says if you only take one thing from the book, take 100% responsibility for everything in your life.

Gery Keller is already wealthy and super successful. He is the founder of Keller Williams, which is the largest real estate company in the world. What wisdom does he have to share from his success? Focus. Have a priority not priorities. The book, "The ONE Thing" is very actionable in helping you to identify your ONE thing—whereby doing your one thing, everything else becomes easier or unnecessary.

Lastly, "Rework", written by Jason Fried and David Heinmeier Hansson, takes a counter intuitive approach to work. Read the other books, then read this book as there are several business ideas and applications to put in to practice what you learn. Some nuggets from this book: Do less, planning is guessing, kill the to-do list, out teach the competition, think like a chef, small bets vs one big gamble, ignore the details early on, sell your by-products, pick a fight, say no by default and welcome obscurity.