Here’s another one that I think is good advice for scientists:

“Reading, after a certain age, diverts the mind too much from its creative pursuits. Any man who reads too much and uses his own brain too little falls into lazy habits of thinking.”
–Albert Einstein

The idea is one I’ve long held, though it flies in the face of conventional ideas: reading is useful to learn only what other people have thought. After a while, however, you need to move on to creating your own thoughts, using other people’s thoughts only as stepping stones – if at all. There’s no novelty to be found in the thoughts of others – they’re better at thinking in their own ways than you are.

Concentrating too much on the past will only prevent you from expending the effort in more useful ways.