If you do not change the direction in which you are going, you will end up where you are headed.

They must often change, who would be constant in happiness or wisdom.

By three methods we may learn wisdom: first, by reflection, which is noblest; second, by imitation, which is easiest; and third, by experience, which is the most bitter.

By three methods we may learn wisdom: first, by reflection which is noblest; second, by imitation, which is the easiest; and third, by experience, which is the bitterest.

He who knows all the answers has not been asked all the questions.

To know that you know, and to know that you don't know - that is the real wisdom.