Maybe it is like slowly heating/boiling the frog in hot water.

From Snopes:

"The frog’s body temperature follows its surroundings. If you put the frog directly in boiling water, it will sense the heat immediately and jump out. But when you heat the water slowly, the frog keeps adjusting to the rising temperature. When the heat is too much for the frog to take, it is too late. The frog collapses and dies."