The principle of right thinking is an idea that is neither old nor new, but it’s always relevant. It has been repurposed, resold, and refurbished for each generation. British philosophical writer James Allen, regarded as the father of the modern self-help era, penned a remarkable treatise on the power of thought in 1903. His 50-page pocketbook, “As a Man Thinketh,” is perhaps the most concise and poignant articulation of the effect of thought on circumstance. There are hundreds of quotable lines in this small book, but the message can be summed up in its most quoted passage: “As a man thinketh in his heart, so shall he be.” This serves as an allusion to Proverbs 23:7: “For as he thinks in his heart, so is he.” It’s a profound statement on the nature of reality and the age-old question of whether we’re the victims of circumstance or the creators of …