Retold in American Sign Language (ASL).
"They say that if you put a frog into a pot of boiling water, it will leap out right away to escape the danger."
But, if you put a frog in a kettle that is filled with water that is cool and pleasant, and then you gradually heat the kettle until it starts boiling, the frog will not become aware of the threat until it is too late. The frog's survival instincts are geared towards detecting sudden changes."
Also see The Goats and the Bridge: a fable.