My higher level students are given more challenging vocabulary worksheets when they finish set tasks. This keeps them busy and helps expand their vocabulary. Once you master the grammar, and incidentally many migrants do not, no matter how long they live in Australia, once you master the grammar then it's all about vocabulary. English has the largest vocabulary of all the world's languages. If language is all about communication and self expression then the more words you know, the better.
Anyway, I digress. A recent gap fill worksheet was about friends and one of the phrases to be used to complete a sentence was fair weather friend. None of the students knew what this was until I explained it, and then of course there were numerous "a-ha" moments as a succession of pennies dropped.
I'm currently re reading The Four Loves by C.S.Lewis. Here is just one of the many profound things he has to say about friendship.
The mark of a perfect friendship is not that help will be given when the pinch comes (of course it will) but that, having been given, it makes no difference at all. It was a distraction, an anomaly.
If you have at least one real friend, you should be thankful. I am.