The acts of the mind, wherein it exerts its power over simple ideas, are chiefly these three: 1. Combining several simple ideas into one compound one, and thus all complex ideas are made. 2. The second is bringing two ideas, whether simple or complex, together, and setting them by one another so as to take a view of them at once, without uniting them into one, by which it gets all its ideas of relations. 3. The third is separating them from all other ideas that accompany them in their real existence: this is called abstraction, and thus all its general ideas are made.

John Locke

An Essay Concerning Human Understanding, 1690

Every young farmboy knows that the hardest and noblest wood has the narrowest rings, that high on the mountains and in continuing danger the most indestructible, the strongest, the ideal trees grow.

Hermann Hesse

Wandering, 1920

Being an amateur, a free lance who never held any academic post or had any professional status, I had the rather unusual advantage of considering problems with an open mind, unbiased by traditional textbook ideas that had remained untested against facts.

Ralph Bagnold

Sand, Wind, and War: Memoirs of a Desert Explorer, 1991

Perseverance - a lowly virtue whereby mediocrity achieves an inglorious success.

Ambrose Bierce

The Devil's Dictionary, 1911