question for someone with pro knowledge of psychology

I know there is a technical term for this but what is it?

Someone says something or writes something, it is not true, but everyone repeats it and it becomes a "fact". What is this called? Besides idiotic?

Mayb a mass effect or something like that? ;)

Is the author ignorant of their mistake or intentionally deceiving people?

Does the word refer to the misconception, or the act of it becoming a popular belief?

Is the word apocryphal ? If I'm correct, what do I win? I want chocolate.

No, that's not it. Its more like the "something" effect. It doesn't matter if author is aware or not the effect is that if people see it enough it becomes truth.

Korchann it is some name of someone effect. I can't remember.

Illusionary Truth effect?

This has been renamed the "Trump effect."

Sarno won!

So mayb “Goebbels effect” ? Cos it was Joseph Goebbels who said it.. well that’s what comes up on wiki after I did put it on net in Czech language lol
Anyway I’m of to bed gn;)

gn people

Its called "Illusory truth effect", or in common word sense simple "repetition". First to me know described effect of such psychological influence was in Roman Empire time, where one of senators always was ending his speech with words: ".. and by the way: Carthaga has to be destroyed".

This effect is based on bias - like almost every manipulation...

If you are interested also check "creeping determinism" which is also valid on field of this effect.

Other, imo much more useful study of this subject, is called Overton Window.

Note:
Quite interesting is, that usually people with paranoid and narcistic tendencies are able to manipulate through emotions surrounding with lie, despite they are able to see facts, but such bias simply doesnt fit into their self perception, reality they want to live in, etc.. and this final effect can make bias in people who are rational and normally understand their emotions.