Russell Conwell 
The Key to Success [EPUB ebook] 

People are thinking, but they can think much more. The housewife is thinking about the chemical changes caused by heat in meats, vegetables, and liquids. The sailor thinks about the gold in sea-water, the soldier thinks of smokeless powder and muffled guns; the puddler meditates on iron squeezers and electric furnaces; the farmer admires Luther Burbank’s magical combinations in plant life; the school-girl examines the composition of her pencil and analyses the writing-paper; the teacher studies psychology at first hand; the preacher understands more of the life that now is; the merchant and manufacturer give more attention to the demand. Yes, we are all thinking. But we are still thinking too far away; even the prism through which we see the stars is near the eyes. The dentist is thinking too much about other people’s teeth.
This book is sent out to induce people to look at their own eyes, to pick up the gold in their laps, to study anatomy under the tutorship of their own hearts. One could accumulate great wisdom and secure fortunes by studying his own finger-nails. This lesson seems the very easiest to learn, and for that reason is the most difficult.