Expressing “本来以为……但是没想到……”

If we previously held a belief, opinion, or understanding, but later discovered we were wrong, or learned new information that challenges our understanding, we can use this structure to express that nuance.

It will closely translate to:

“I originally thought that...., but I didn't expect that....”.

First, let's break down the new words that make up this structure.  Each of these phrases are super duper useful, so let's see how they are used individually.  We have:

1. 本来 -- originally

2. 以为 -- "I had thought that.."

3. 没想到 -- "I didn't expect.." 

(1) 本来 Means Originally  

Wǒ běnlái yào 7 diǎn qǐchuáng, dànshì yīnwèi wǒ zuótiān shuì dé tài wǎnle, suǒyǐ wǒ 7 diǎn méi qǐlái.
我本来要7点起床，但是因为我昨天睡得太晚了，所以我7点没起来。
I was originally supposed to get up at 7:00, but I didn't get up at 7:00 because I slept in so late yesterday.  

(2) 以为 Thought or Considered, but Was Wrong.

Wǒ yǐwéi nǐ hěn ài wǒ, dànshì wǒ cuòle, nǐ bù ài wǒ.
我以为你很爱我，但是我错了，你不爱我。
I thought you loved me very much, but I was wrong, you don't love me. 

(3) 没想到=没有想到 Didn't Expect

Wǒ méi xiǎngdào tā huì qù kàn diànyǐng, yīnwèi tā xiàwǔ gàosù wǒ tā méiyǒu shíjiān.
我没想到他会去看电影，因为他下午告诉我他没有时间。
I didn't expect him to go to watch the movie, because this afternoon he told me he didn't have time. (but he DID watch the movie！) 

Now, let's combine these words together to make some really common grammar sets.  These phrases are very useful when you want to express a change in your feelings or something you didn't expect.

Subject + 本来+ …… 但是…… Originally ……， But ......

Wǒ běnlái hěn shēngqì, yīnwèi wǒ de gǒu chīle wǒ de xiézi, dànshì xiàwǔ wǒ hé péngyǒu yīqǐ qù mǎile yīshuāng xīn xiézi, wǒ xiànzài juédé hěn kāixīn. 我本来很生气，因为我的狗吃了我的鞋子，但是下午我和朋友一起去买了一双新鞋子，我现在觉得很开心。 I was originally angry, because my dog ate my shoes, but in the afternoon I went to buy a new pair of shoes with my friends and I feel very happy now.

Wǒ běnlái bù xǐhuān yóuyǒng, dànshì péngyǒu shuō yóuyǒng duì shēntǐ hěn hǎo, xiànzài wǒ hěn xǐhuān yóuyǒng, wǒ yīgè xīngqī yóu yīcì. 我本来不喜欢游泳，但是朋友说游泳对身体很好，现在我很喜欢游泳，我一个星期游一次。 I didn’t like swimming originally, but my friend said that swimming is good for you. Now I like swimming very much. I swim once a week.

Subject+本来以为……但是没想到…… Originally Thought……，but Didn't Expect......

Tā běnlái yǐwéi zhège diànyǐng hěn wúliáo, dànshì méi xiǎngdào tā hěn hǎowán. 她本来以为这个电影很无聊，但是没想到它很好玩。 She originally thought the movie would be boring, but she didn't expect it to (actually) be fun.

Wǒ běnlái yǐwéi jīnnián kěyǐ qù zhōngguó lǚyóu, suǒyǐ wǒ hěn gāoxìng, dànshì méi xiǎngdào yīnwèi COVID19, wǒmen bùnéng qù zhōngguóle, wǒ juédé hěn shīwàng. 我本来以为今年可以去中国旅游，所以我很高兴，但是没想到因为COVID19，我们不能去中国了，我觉得很失望。 I originally thought that I would be able to travel to China this year, so I was happy, but I didn't expect we wouldn't be able to go to China because of COVID19... I was so disappointed.

Wǒ běnlái yǐwéi wǒ bùnéng hé jiārén yīqǐ guòjié, yīnwèi wǒ méiyǒu mǎi dào huí jiā de chēpiào, suǒyǐ wǒ hěn nánguò, dànshì méi xiǎngdào wǒ de nán péngyǒu yǐjīng mǎihǎole huí jiā de chēpiào. Wǒ tài kāixīnle! 我本来以为我不能和家人一起过节，因为我没有买到回家的车票，所以我很难过，但是没想到我的男朋友已经买好了回家的车票。我太开心了！ I originally thought I couldn't spend the holiday with my family and I was very sad because I didn't get a ticket home. But I didn't expect my boyfriend had already bought tickets. I am so happy!