Why do we say "It Never Rains But It Pours"?

Meaning:

When you've been waiting a long time for something, sometimes too much arrives. For example, a farmer waiting for rain who gets his crops damaged by a heavy storm.

Background:

No doubt, this sentiment has been expressed for many thousands of years. However, one early use is recorded in 1726 when John Arbuthnot wrote It Cannot Rain But It Pours.

More expressions and their source

Challenge yourself with BookBrowse Wordplays