过去不在我们身后,而在我们之内。
文章必须对天下人有益处。
 我从未遇到过一小时阅读不能解除的痛苦。
In the end, we only regret the chances we didn't take.
The mathematician does not study pure mathematics because it is useful; he studies it because he delights in it and he delights in it because it is beautiful.