If you spend too much time thinking about a thing, you'll never get it done.

If you think a thing is impossible, you'll make it impossible.

I cannot teach anybody anything, I can only make them think.

To study and not think is a waste. To think and not study is dangerous.

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.

The whole of science is nothing more than a refinement of everyday thinking.

A public-opinion poll is no substitute for thought.

If everybody is thinking alike, then somebody isn't thinking.

He who thinks little, errs much.

Don't think about what you've left behind.