Boiled Frog
An anecdote describing a frog in a pot of water where the water's temperature is gradually raised to the point of killing the frog without their noticing, but if the frog is placed instantly in hot water, it would jump out immediately.
Origin
The metaphor traces to 19th-century physiology. In 1869, German physiologist Friedrich Goltz showed that a decerebrate frog would remain in gradually heated water while an intact frog escaped — an observation later embellished by an 1882 Johns Hopkins University experiment claiming a live frog could be boiled without moving. Modern biologists have debunked this. The story entered management culture through Peter Senge's 1990 book The Fifth Discipline, which used it to illustrate how organisations fail to respond to incremental competitive threats.