A little old time-y, but still incredibly powerful and relevant, James Allen's As a Man Thinketh aims to illustrate just how powerful our thoughts are. If you doubt the power of thoughts and their ability to help you create any result that you want (and also the results you want to avoid so badly that you can't stop thinking about them...), then this book is a must read.
The book is short, but packed with wisdom. The best thing about this little classic is that it causes us to acknowledge that we can control our thoughts and by thus controlling our thoughts, we can control our outcomes. This means that we can literally and seriously create any result that we want in our life.
Here are a few of my favorite quotes from the book:
"All that a man achieves and all that he fails to achieve is a direct result of his own thoughts."
"A man can only rise, conquer, and achieve by lifting up his thoughts. He can only remain weak, and abject, and miserable by refusing to lift up his thoughts."
"Dream lofty dreams, and as you dream, so shall you become."