“The key to every man is his thought.”

“Of all knowledge, the wise and good seek most to know themselves.”

“Do you want to know the man against whom you have most reason to guard yourself? Your looking-glass will give you a very fair likeness of his face.”

“The first step to knowledge is to know that we are ignorant.”

“The more you practice what you know, the more shall you know what to practice.”

“Thinking is the hardest work there is, which is the probable reason why so few engage in it.”