A blemish may be removed from a diamond by careful polishing, but evil words once spoken cannot be effaced.
If you know, say you know. If you don't know, say you don't know.
He who knows all the answers has not been asked all the questions.
First there must be order and harmony within your own mind.
Study the past if you would define the future. I am not one who was born in the possession of knowledge; I am one who is fond of antiquity, and earnest in seeking it there. Learning without thought is labor lost; thought without learning is perilous.
Future generation is the most important thing.