To do much clear thinking a person must arrange for regular periods of solitude when they can concentrate and indulge the imagination without distraction.

There is no limit to which a man will not go to avoid thinking.

The trouble with most people is that they quit before they start.

The man who doesn't make up his mind to cultivate the habit of thinking misses the greatest pleasure in life.

Hard knocks have a place and value, but hard thinking goes farther in less time.

Loneliness is one thing, solitude another.