True knowledge and insights first come from thinking and doubting.

——Rockwell

Spending time on thinking is the most time-saving thing.

——Cousins

Thinking is the self-talk of the soul.

——Plato

Those who are not determined to cultivate the habit of thinking will lose the greatest joy in life.

——Edison

The development of the thinking world, in a sense, is the continuous getting rid of surprise.

——Einstein

Doubts grow with knowledge.

——Goethe

Greatness is not only earth-shattering in his career, he often thinks deeply and quietly.

——Krylov

It is embarrassing to fight against one's own heart, but this kind of victory is a sign of a thoughtful person.

——Democritus