Scylla and Charybdis are two sea monsters of Greek mythology noted by Homer. Later Greek tradition sited them on opposite sides of the Strait of Messina between Sicily and the mainland of southern Italy. They were said to be located close enough to each other that they posed an inescapable threat to passing sailors. Avoiding Charybdis meant passing too closely to Scylla, and vice versa. Scylla was said to be a creature who was rooted to one spot in the ocean, and regularly ate sailors who passed by too closely. She was described by Homer in The Odyssey as having six heads perched on long necks along with twelve feet. In Ovid's Metamorphoses, she was depicted as having the upper body of a nymph, with her mid section composed of dog's heads. Charybdis was depicted with a single gaping mouth that sucked in huge quantities of water, and belched them out three times a day, creating whirlpools. According to myth, Odysseus was forced to choose which monster to confront while passing through the strait. He chose to pass by Scylla and lose only a few sailors, rather than risk the loss of his entire ship into the whirlpool. Jason and the Argonauts were able to navigate through without incident, with Hera's assistance. Aeneas was able to bypass the deadly strait altogether. [Thank you, Wikipedia.] Incidentally, JoeRay, I think you referenced this myth in answer to another question, which I found after your added detail above. It is true that a "Scylla and Charybdis" connection can be made to several modern sayings ... ~ I am caught "between a rock and a hard place." ~ It seems you are "damned if you do, damned if you don't." ~ Now we are stuck "between the devil and the deep blue sea." An example using your phrase ... ~ For Yahoo, choosing between Microsoft and Google must seem like "sailing between Scylla and Charybdis."

I had wondered if JoeRay had been watching Prison Break! They use that reference in the fourth season. I'll add a bit more random stuff to Joe's answer - it's been a long while since reading it, so I've lost track of the series of events. (Doesn't help that the story is told in a pile of flashbacks - and I do mean the original poem.) Thanks to Circe and Teiresias, Odysseus was given a plan on how to get home safely. Which meant passing between Scylla and Charybdis - and therefore sacrificing what they have, ie. several shipmen - before they could continue. So it's not exactly being "stuck" between a rock and a hard place. The analogy is that you must go through a situation where either choice means you lose out. You're not trapped, but you must keep going or lose everything. So you choose the lesser of two evils. If you have time and patience I really recommend reading Homer, especially in verse. The verse translations are harder to find, but much better than the common prose versions.

Nothing to add to Joe's answer, except that if you use this reference to mythology, be sure you are speaking with someone who is very well educated. Most people in the US will not understand "Scylla and Charybdis." But I love Joe's last example :D

I just want to add that Scilla and Cariddi are in the south of Italy and I've been there so if you need other details... (Scilla is a beautiful place especially in summer) =)