Self-fulfilling prophecy .
(I am not aware of a single-word equivalent in English.)
english.stackexchange.com/users/300/RegDwigнt
I remember my cousin, who is a psychologist, mentioned about the term "Pygmalion effect".
Here is a definition from Wikipedia: The Pygmalion effect , or Rosenthal effect , refers to the phenomenon in which the greater the expectation placed upon people, often children or students and employees, the better they perform.
The effect is named after Pygmalion, a Cypriot sculptor in a narrative by Ovid in Greek mythology, who fell in love with a female statue he had carved out of ivory.
The Pygmalion effect is a form of self-fulfilling prophecy, and, in this respect, people with poor expectations internalize their negative label, and those with positive labels succeed accordingly.
Within sociology, the effect is often cited with regards to education and social class.
english.stackexchange.com/users/127/Mehper C. Palavuzlar
The Yankee's nascent loss...
english.stackexchange.com/users/460/Chris Noe
Depending on exact context, you might get away with "conjure".
Even "will" might do.
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If someone says "...
", and everyone starts believing it, ...
and it actually happens —
what is the word for that?
( verb ) predict early 17th century: from Latin praedict- ‘made known beforehand, declared,’ from the verb praedicere, from prae- ‘beforehand’ + dicere ‘say.’
He predicted the Yankees were going to lose (and everyone believed it), and they did lose.
Synonym: foretell
(past tense, foretold )
However, logically there is no way to prove that any prediction or foretelling has anything at all to do with any outcome.
You might argue that predictions have psychological effects which may influence an outcome, but that's very difficult if not impossible to prove.
But to answer the question more specifically, the noun forms for them would be: prediction forecast
english.stackexchange.com/users/273295/Bread
Besides the already mentioned self-fulfilling prophecy , the closest things that come to my mind are: lack of confidence diminished self-esteem which are rather the cause to make happen what you described.
english.stackexchange.com/users/519/stacker
In the Bible, the verb to call means "to speak something into existence", but it only refers to God.
english.stackexchange.com/users/46567/kjcox
If someone says "the Yankees are going to lose", and everyone starts believing it, including the players, and it actually happens — what is the word for that?
What word means "to speak something into existence"?
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<single-word-requests><nouns>
english.stackexchange.com/questions/4274
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It is possible that there is no single-word equivalent in English. However, some options include "conjure" or "self-fulfilling prophecy". Additionally, the verb "to call" means "to speak something into existence" but it only refers to God. Self-fulfilling prophecy is the phrase for this, although not a single word. The  Pygmalion effect refers to the phenomenon in which the greater the  expectation placed upon people, often  children or students and employees,  the better they perform. "Conjure" or "forecast" could possibly be used.  In the Bible, the verb ' to call'  means "to speak something into existence", but it only refers to God.
"Self-fulfilling prophecy" is an expression used in this context. However "to conjure" or 2to call" may be used depending on the context. It is possible that there is no single-word term to describe this concept. However, some options include "conjure" or "self-fulfilling prophecy". Additionally, the verb "to call" means "to speak something into existence" but is reserved solely for God.
I am not aware of a single-word equivalent in English. Self-fulfilling prophecy is the phrase for this, although not a single word.  The  Pygmalion effect refers to the phenomenon in which the greater the  expectation placed upon people, often  children or students and employees,  the better they perform. "Conjure" or "forecast" could possibly be used.  In the Bible, the verb ' to call'  means "to speak something into existence", but it only refers to God.
"Speaking something into existence" might be called a "self-fulfilling prophecy" or "conjuring". In the Bible, "to call" means to "speak something into existence" but only refers to God. It is possible that there is no single-word term to describe this concept.