Later, the author writes:
Lackadaisical attention--slipshod thinking—diffused interest—scattering of mental forces, all these get us nowhere. The Jack-of-all-trades is a failure in the twentieth century. The big rewards of this age go to the man who can do one thing supremely well. That-means concentration.I need to practice more:
Try to hold a chosen topic of thought for a fixed period of time. Do not be too ambitious... Try it on the following topics: "How I spent my last birthday." "My favorite book." "The best moving-picture I ever saw." "The most inspiring lecture I ever heard"... Be content with a minute, at the outset less, perhaps, if your pride permit.Via Feld.