Expressing "no wonder"
怪不得 (guàibude) can be used to express that the speaker finds something unsurprising. It can be used alone or in a variety of different structures, as shown below. 难怪 (nánguài) is another way to express the exact same thing.
Emphasis on 怪不得 / 难怪
怪不得 is used to convey the speaker's newfound understanding of a situation, having recently acquired some new information that, in his opinion, explains it.
Reason ，怪不得 / 难怪 + [Observation]
怪不得 can be replaced with 难怪 in the structure without altering its meaning.
- 小张 请假 了，怪不得 今天 没有 看到 他 。Little Zhang asked for vacation time, no wonder I haven't seen him today.
- 天天 迟到 ，怪不得 他 被 炒鱿鱼 了 。He's late for work every day. No wonder he got fired.
- 她 是 你 妹妹 ？难怪 你们 长 得 这么 像 。She's your younger sister? No wonder you two look so much alike.
- 你 手机 没电 了 ？怪不得 我 打 不 通 。Your cell phone is out of power? No wonder my call wouldn't go through.
- 你 放 了 醋 ？难怪 这么 难吃 ！You put vinegar in it? No wonder it tastes so bad!
Emphasis on 原来
怪不得 / 难怪 + [Observation] ，原来 (+ 是) + Reason
- 难怪 学生 都 不 喜欢 这个 老师 ，原来 他 的 作业 太 多 了 。No wonder the students don't like this teacher. He gives too much homework.
- 怪不得 你们 这么 高兴 ，原来 是 要 结婚 了 。No wonder you two look so happy. You are getting married.
- 难怪 这里 人 这么 多 ，原来 在 打折 。No wonder there are so many people here. There's a sale going on.
- 怪不得 她 拉肚子 ，原来 她 昨天 又 吃 火锅 了 。No wonder she got a diarrhea. She went to eat hotpot again yesterday.
- 怪不得 他 没 告诉 我 ，原来 是 不 想 让 我 担心 。No wonder he hasn't told me. He doesn't want me to worry about this.
The Other Meaning of 难怪
This usage is definitely less common, but sometimes 难怪 is a combination of the 难 + Verb pattern and the verb 怪, meaning "to blame." In this case, the meaning is totally different. Although it's not as common, and you shouldn't need to worry about it too much, we include it here because if you ever run into and think that 难怪 can only ever have one meaning, it can totally throw you for a loop.
A few examples:
- 这 也 难怪 他 ，他 这么 小 。We can't really blame him. He's so young.
- 这 也 难怪 大家 ，是 我们 通知 晚 了 。We can't really blame everybody. It was such short notice.
When used in this way it expresses that the speaker assigns no blame in the situation he is describing. Sometimes the specific person undeserving of blame is mentioned directly after 难怪, but not always.
Sources and further reading