1. Learning without thinking is useless, and thinking without learning is dangerous. 2, review the old and know the new, you can be a teacher. 3, learn from time to time, not to mention? Is it not delightful to have friends coming from distant quarters? Is he not a man of complete virtue, who feels no discomposure though men may take no note of him? 4. Those who know are not as good as those who know, and those who are good are not as good as those who enjoy. 5, a threesome must have my teacher, choose the good one and follow it, and change the bad one.