Creeping normality

Creeping normalcy (also called gradualism, or landscape amnesia) is a process by which a major change can be accepted as normal and acceptable, if it happens slowly through small, often unnoticeable, increments of change.
The change could otherwise be regarded as dangerous and objectionable if it took place in a single step or short period.

The boiling frog is a fable describing a frog being slowly boiled alive.
If a frog is put suddenly into boiling water, it will jump out, but if the frog is put in tepid water which is then brought to a boil slowly, it will not perceive the danger and will be cooked to death.
The story is often used as a metaphor for the inability or unwillingness of people to react to, or be aware of sinister threats that arise gradually rather than suddenly.

The opposite effect is the Butterfly effect.

If people are confortable enough, they will not revolt. A dictator can keep millions docile as he strips their rights slowly over time, just by giving them some rewards, food and distractions like entertainment.
This is also called “bread and circus”.

A great wave of oppressive tyranny isn’t going to strike, but rather a slow seepage of oppressive laws and regulations from within will sink the American dream of liberty.
– George Baumler

Links

https://academyofideas.com/2015/11/fear-and-social-control
“They Thought They Were Free”, is based on interviews with normal Germans who lived during the Nazi regime.
The following quote comes from one of the German’s interviewed, where he discusses why he thought that more ordinary Germans didn’t take a stand against the rise of the Nazi government:

“One doesn’t see exactly where or how to move. Believe me, this is true. Each act, each occasion, is worse than the last, but only a little worse… You wait for one great shocking occasion, thinking that others, when such a shock comes, will join with you in resisting somehow…
But the one great shocking occasion, when tens or hundreds or thousands will join with you, never comes. That’s the difficulty. If the last and worst act of the whole regime had come immediately after the first and smallest, thousands, yes, millions would have been sufficiently shocked… But of course this isn’t the way it happens. In between comes all the hundreds of little steps, some of them imperceptible, each of them preparing you not to be shocked by the next…
And one day, too late, your principles, if you were ever sensible of them, all rush in upon you. The burden of self-deception has grown too heavy, and some minor incident… collapses it all at once, and you see that everything - everything - has changed…
Now you live in a world of hate and fear, and the people who hate and fear do not even know it themselves; when everyone is transformed, no one is transformed…
– Milton Mayer, They Thought They Were Free