In 1902, self-taught British philosopher and author James Allen published this inspirational essay based on the Bible verse "As a Man thinketh in his heart, so is he." This slender volume (only 68 pages) has been a popular classic ever since. Allen preached the importance of people taking responsibility for themselves and their actions as well as using determination to improve the mind.

The most frequently quoted lines from the book include: "Men do not attract what they want, but what they are" and "A man is literally what he thinks, his character being the complete sum of all his thoughts."