I have heard this saying all my life. And heard again a couple days ago, though I’m not sure who said it.
I decided that it made no sense to me that straw could break a camel’s back so I looked it up and Wikipedia said:
Straw that broke the camel’s back
From Wikipedia, the free encyclopedia
The idiom the straw that broke the camel’s back is from an Arab proverb about loading up a camel beyond its capacity to move. This is a reference to any process by which cataclysmic failure (a broken back) is achieved by a seemingly inconsequential addition (a single straw). This also gives rise to the phrase “the last straw”, used when something is deemed to be the last in a line of unacceptable occurrences. A variation of this idiom is “the straw that broke the donkey’s back”.
One of the earliest usages of this phrase was in Charles Dickens’s Dombey and Son where he says “As the last straw breaks the laden camel’s back”, meaning that there is a limit to everyone’s endurance, or everyone has his breaking point. Dickens was writing in the nineteenth century and he may have received his inspiration from an earlier proverb, recorded by Thomas Fuller in his Gnomologia as ‘Tis the last feather that breaks the horse’s back.’
Retrieved from “http://en.wikipedia.org/wiki/Straw_that_broke_the_camel%27s_back”
Now, I understand!