Norma Rae (1979)
In the film : Norma Rae writes the word "UNION" on a piece of cardboard, stands on her work table, and slowly turns to show the sign around the room. One by one, the other workers stop their mill machines, and eventually, the entire room becomes silent.
Similar situation : Juror #8 in 12 Angry Men (1957)
In real-life : You find the courage to raise the only dissident voice, sincerely speaking for your beliefs, and then, one by one, your (at first) reluctant comrades share your opinion and express their solidarity or their agreement.