Lü Meng was a general of the state of Wu during the Three Kingdoms Period (220-180). Born in a poor family, he did not have the chance to go to school when he was a child. When he was grown, he joined the army, and there was even less time for reading.

Once, the king of Wu summoned Lü and said to him, "You're a big general now. You'd better read some books to widen your horizons."

"I am so busy with military work," Lü replied. "I'm afraid I have little time to read."

"Are you busier than I am?" the king said. "Even I find time to read books on the art of war, and they've benefited me greatly. Read more about the experience of our predecessors. You'll make greater progress."

Accepting the king's advice, Lü set about reading history and military writings. One day, chief commander Lu Su visited Lü Meng. Lu Su had looked down on Lü Meng in the past. He was surprised to find Lü had become so knowledgeable.

"I thought you only knew how to fight!" Lu Su said. "You are not the Lü Meng you used to be."

"You should always look at a person with fresh eyes – even if you've only been apart three days," Lü Meng replied.

Lü Meng's remarks inspired the idiom "guā mù xiāng kàn", or "guā mù xiāng dài". It's used to express astonishment by others' fabulous progress or improvement and increased respect for him or her.

guā mù xiāng kàn
刮目相看

    三国时期（220－280），吴国有一个叫吕蒙的将军。吕蒙出生在穷苦人家，小时候没有机会上学。长大后，他参了军，看书的时间更少了。

    一次，吴国的皇帝召见吕蒙，对他说：“现在你是大将军了，应该多看看书开阔眼界。”

    吕蒙回答道：“军中的事务这么忙，我恐怕没有时间读书。”

    吴国的皇帝说：“你难道比我还忙吗？我常常抽空阅读兵书，从中得到了不少好处。多看看前人的经验之谈，你会有更大的进步。”

    吕蒙接受了皇帝的建议，从此开始专心阅读，看了很多历史和军事书籍。一天，主帅鲁肃来拜访吕蒙，惊讶地发现吕蒙变得很有学问。曾经非常轻视吕蒙的鲁肃说：“我以为你只会打仗，没想到你这么博学。你已经不是过去的那个吕蒙了！”

    吕蒙回答道：“即使你和别人只分开了三天，三天后再遇到他时，也不能用三天前的老眼光来看待他。”

    我们从吕蒙的话中得到了成语“刮目相看”，也叫“刮目相待”，用它来形容别人有了很大的进步，要用新的眼光来看待。

dà zhì ruò yú
大智若愚
a man of great wisdom often appears slow-witted

yīn xiǎo shī dà
因小失大
try to save a little only to lose a lot; be penny wise and pound foolish; be wise or careful in small matters but not in important ones
sān cháng liǎng duǎn
三长两短
unexpected misfortune or calamity; mishap

jiǔ sǐ yī shēng
九死一生
escape by the skin of one's teeth; avoid death by a hair's breadth; narrowly escape from death

cǐ qǐ bǐ fú
此起彼伏
as one falls, another rises; (of sound) rise one after another; continually rising and falling

jiǎ gōng jì sī
假公济私
use public office for private gain; exploit public office for private ends

Source: China Internet Information Center