外面下雪啦，怪不得这样冷。

No wonder it's so cold – it's snowing outside.

我和他见过面，怪不得有些面熟。

I've met him before – no wonder he looks familiar.

原来他离开上海了，怪不得我总没有碰见他。

No wonder I've not bumped into him – it turns out he left Shanghai.

怪不得好久没见到你了。

No wonder I haven't seen you for so long.

你自己不好，怪不得别人。

You can't blame others for your own failings.