blow hot and cold

Example: “The investors have been blowing hot and cold on the project for months.”

Origin: Traces to one of Aesop's fables, "The Satyr and the Traveler": a satyr, sharing shelter with a traveler on a cold night, watches the man blow on his hands to warm them and later blow on his soup to cool it, and ends the friendship on the spot, unable to trust someone who does opposite things with the same breath. Erasmus recorded the Latin version of the saying in his 1508 Adagia, and the English idiom is established by the first half of the 1600s. The fable's moral survives intact in the phrase: someone who "blows hot and cold" flips between enthusiasm and indifference so readily that neither can be trusted as their real position.