If you don’t make mistakes, you’re not working on hard enough problems. And that’s a big mistake.

解析：教导学生，不到他想弄明白而不得的时候，不去开导他；不到他想出来却说不出来的时候，不去启发他。

The time which we have at our disposal every day is elastic; the passions that we feel expand it, those that we inspire contract it; and habit fills up what remains.