The modal adverb 简直
The modal adverb (语气副词) expresses subjective judgment or assurance toward an action.
The adverb 简直 
gives a touch of exaggeration. It can be used in different ways:
1) In an expression of surprise or amazement. We state it before a predicate, which is expressed by a verb or an adjective.
gives a touch of exaggeration. It can be used in different ways:
1) In an expression of surprise or amazement. We state it before a predicate, which is expressed by a verb or an adjective. Pay attention
After 简直, we can only use the adverbs 太 or 极了 .
or 极了 .Examples
我简直不明白，你为什么没有告诉我？
I just don't understand why you didn't tell me?
wǒ jiǎnzhí bù míngbái, nǐ wèishénme méiyǒu gàosù wǒ
你简直太漂亮了！
You're simply beautiful!
nǐ jiǎnzhí tài piàoliang le
2) before comparative constructions such as 像 or 跟…一样 to indicate similarities.
or 跟…一样 to indicate similarities.Examples
你汉语说得很流利，简直跟中国人一样！
You speak Chinese fluently, just like the Chinese!
nǐ hànyǔ shuō de hěn liúlì, jiǎnzhí gēn zhōngguórén yíyàng
我叔叔说话简直像外国人
My uncle speaks just like a foreigner
wǒ shūshu shuōhuà jiǎnzhí xiàng wàiguórén
3) when expressing a personal opinion. We should use the verb 是 after 简直, and then state the speaker's opinion.
after 简直, and then state the speaker's opinion.Examples
他活下来了，简直是奇迹！
It’s a miracle that he survived!
tā huóxiàlái le, jiǎnzhí shì qíjī
他简直是个骗子
He's just a liar
tā jiǎnzhí shì ge piànzi
4) to indicate that some action almost happened.
Examples
他的变化太大，我简直认不出来了
He has changed so much that I can hardly recognize him
tā de biànhuà tài dà, wǒ jiǎnzhí rèn bù chūlái le
他高兴得简直要哭出来
He was so happy that he almost cried
tā gāoxìng de jiǎnzhí yào kū chūlái
After 简直, we can use constructions that actions in progress such as 在…呢 to indicate that the action is happening right now.
to indicate that the action is happening right now.Examples
你不会成功，简直在扔钱呢
You won't make it, you're just throwing money away
nǐ bú huì chénggōng, jiǎnzhí zài rēng qián ne