Quite the thing

We can derive the meaning of this word from the context very easily because we have been exposed to this situation so many times: a forbidden relationship forces a couple to run away in secrecy. This is what LaPolla has termed "habit"; in this case the habit of a narrative we have been exposed to so many times.

I think this is indeed a protypical context; we just need to consider that reading a book is in fact a generally common situation for educated people of any age, but the second example is more typical of grown-up people who have to worry about such matters as doing the groceries. The final example is fitting to most ages on the whole, since minors could say that that is their plan because it is a family tradition to do so over the weekends.