no wonder, it's no wonder, (it's ) small wonder 与 it's not surprising 这几个说法意思相同，都指“……不令人奇怪；难怪”。

• (It's) No wonder (that)/It's not surprising that you can't sleep — you've eaten too much.
  难怪你睡不着，你吃得太多了。
• He was taken ill again, and small wonder/it was not surprising , considering that he had been overworking for years.
  他又生病了，也难怪，他多年来一直超负荷工作。
• He did not go to the concert yesterday. No/Small wonder — he dislikes disgusting pop singers.
  昨天他没去音乐会，这也难怪——他不喜欢那些招人烦的流行歌手。