“Grabbing at straws” (or “grasping,” today the more common form) comes from the very old proverb noted by Samuel Richardson in his novel Clarissa (1748): “A drowning man will catch at a straw, the proverb well says.” The “straw” in this case refers to the sort of thin reeds that grow by the side of a river, which a drowning man being swept away by a fast current might desperately grasp in a futile attempt to save himself. Thus “grasp at straws” has, since at least the 18th century, meant “to make a desperate and almost certainly futile effort to save oneself” (“Bob’s attempt to build a case that the contract was not valid because it contained a split infinitive was just grasping at straws”). “Grasping at straws” is still very much in use in this sense, as by one source quoted by the Associated Press in a recent news story on the economy: “People have to pay the bills, so what we see is people kind of grasping at straws and taking anything that’s available.”