rock

Faced with two equally dangerous or difficult choices or circumstances: “Trying to please two supervisors is like being between a rock and a hard place.” This phrase dates from the early twentieth century.

Also, between the devil and the deep blue sea or Scylla and Charybdis. Between two equally difficult or unacceptable choices. For example, Trying to please both my boss and his supervisor puts me between a rock and a hard place. The rock and hard place version is the newest of these synonymous phrases, dating from the early 1900s, and alludes to being caught or crushed between two rocks. The oldest is Scylla and Charybdis, which in Homer's Odyssey signified a monster on a rock (Scylla) and a fatal whirlpool (Charybdis), between which Odysseus had to sail through a narrow passage. It was used figuratively by the Roman writer Virgil and many writers since. The devil in devil and deep blue sea, according to lexicographer Charles Earle Funk, referred to a seam around a ship's hull near the waterline, which, if a sailor was trying to caulk it in heavy seas, would cause him to fall overboard. Others disagree, however, and believe the phrase simply alludes to a choice between hellfire with the devil and drowning in deep waters.