the straw that broke the camel's back
Possibly from the proverb, recorded by Thomas Fuller in his Gnomologia as "Tis the last feather that breaks the horse's back." This comes from an Arab proverb about loading up a camel beyond its capacity to move, to the scenario of a single straw of grass or hay overwhelming the desert-roaming beast of burden.
- (idiomatic) A small and seemingly insignificant addition to a burden that renders it too much to bear; the small thing which causes failure, or causes inability or unwillingness to endure any more of something.
1848, Charles Dickens, Dombey and Son:
- As the last straw breaks the laden camel's back.