It never rains but it pours

An archaic use of but to introduce an inevitable accompanying circumstance.

It cannot rain but it pours.
[1726 J. Arbuthnot (title)]

The singers were the same as I had heard at the Burletta. ‥‘It never rains, but it pours!’
[1770 C. Burney Music, Men and Manners in France and Italy (1974) 22 July 54]

A wife with a large fortune too. It never rains but it pours, does it, Mr. Thorne?
[1857 Trollope Barchester Towers III. xii.]

I listened to the radio. Ben Gurion had suffered a stroke. ‥It never rains but it pours.
[1979 L. Barnea Reported Missing vii.]

When it rains, it pours, and Matt Sullivan is being flooded out by women who want to have sex with him.
[2002 Washington Post 1 Mar. C5]

Related to: misfortune

Bibliography of major proverb collections and works cited from modern editions is available here.

When something occurs it often does so to excess. For example, First Aunt Sue said she and Uncle Harry were coming for the weekend and then my sister and her children said they were coming too--it never rains but it pours. This expression may have come from either a book by Queen Anne's physician, John Arbuthnot, or an article by Jonathan Swift, both entitled It Cannot Rain But It Pours and both published in 1726.