Creeping normalcy refers to the way a major change can be accepted as the normal situation if it happens slowly, in unnoticed increments, when it would be regarded as objectionable if it took place in a single step or short period. Examples would be a change in job responsibilities or a change in a medical condition.
Jared Diamond has invoked the concept (as well as that of landscape amnesia) in attempting to explain why in the course of long-term environmental degradation, Easter Island natives would, seemingly irrationally, chop down the last tree:
Gradually trees became fewer, smaller, and less important. By the time the last fruit-bearing adult palm tree was cut, palms had long since ceased to be of economic significance. That left only smaller and smaller palm saplings to clear each year, along with other bushes and treelets. No one would have noticed the felling of the last small palm.
See also 
- Shifting baseline
- Boiling frog - creeping normalcy metaphor
- Camel's nose - creeping normalcy metaphor
- First they came... - poem about creeping normalcy under the Nazis
- Slippery slope - an argument, sometimes fallacious
- Salami tactics