From Chapter 2, "Beginner's Traps":

In summary, there are no small problems. Problems that appear small are large problems that are not understood. Instead of tiny details unworthy of the intellectual, we have men whose tiny intellects cannot rise to penetrate the infinitesimal. Nature is a harmonious mechanism where all parts, including those appearing to play a secondary role, cooperate in the functional whole. In contemplating this mechanism, shallow men arbitrarily divide its parts into essential and secondary, whereas the insightful thinker is content with classifying them as understood and poorly understood, ignoring for the moment their size and immediately useful properties. No one can predict their importance in the future.

I recommend this book. Amazon writes:

Although the wisdom contained in this slim, elegant volume is almost a century old, it is as fresh and useful today as it no doubt was then.

See also: Google Books; MIT Press offers some samples, or full text for CogNet subscribers.

Advice for a Young Investigator