There Is No Straw that Broke the Camel's Back

If one were to pile straws on a camel's back, there would be several stress fractures well before it snapped outright. Even before that, there would be extensive muscular damage in the back, and maybe even a herniated disk or two. Not to mention the fact that knee and hip injuries might prevent you from even getting that far.

I like it better as "the sledge hammer that broke the camel's back."

But the real point is that if you want to make a saying to express the fact that a small change has had large results, you should at least use an actual critical phenomenon.

How about: "it was the 1/2 degree F that froze the water." Or maybe: "it was the %1 molarity increase that caused the precipitate to form" (or the more familiar version: "the %1 humidity increase that caused it to rain). Another more obscure option would be: "the 10 uK drop in T that caused the Bose-Einstein condensate."

Now, I know it's just a saying. But let's get the science behind these things right, people.