When you went to get a shot, the words, "This won't hurt a bit," became a conditioned stimulus when they were paired with pain of the shot, the unconditioned stimulus, which was followed by your conditioned response of getting the heck out of there.
Cuando fuiste a inyectarte, las palabras, "Esto no te dolerá nada", se convirtieron en un estímulo condicionado al relacionar con el dolor de la inyección, el estímulo incondicional, seguido de tu respuesta condicionada de salir huyendo del lugar.