Hypodermic Needle Model
Sometimes called the "Magic Bullet" theory, the "Hypodermic Needle Model" of communication posits that messages sent by (primarily) mass media entities can (or according some interpretations, almost always do) influence the thought-patterns and behaviors of the people (passively) receiving those messages on the other end.
This concept is sometimes illustrated by thinking of the message as a bullet and the receiver's brain as the target (hence, a "magic bullet").
Coming up with the right message and delivery vehicle is considered to be key, then, as that's what gives these messages the proper aim and intended outcome.
This idea was more popular back in the early 20th century when mass communication mediums like radio and television were initially being deployed, with potent (and almost magical-seeming) effects: folks were zombified by Hollywood offerings and seemed to be brainwashed or controlled by the Nazis' use of radio messages.
Some of the early research into this concept focused on such propaganda (including campaign messaging for then-US presidential candidate FDR), interpreting the results as clear indications that we're all more or less controlled by our instincts, and the right message sent in the right way can trigger, en masse, the receiving audience's knee-jerk response to—for instance—vote a particular way, come to believe a particular message, or buy a given product.
This perhaps understandably became a huge focus of research for several decades, as the idea that even smart, thoughtful people could be manipulated via this approach was both appealing (if you were keen to be a manipulator) or worrying (if you were interested in protecting people from such manipulations).
Later research, beginning mid-century, seemed to debunk most of the thinking and findings underpinning this model (including a variation of it that posited bullet-like messages hit influential people before then trickling down to everyone else) as many of the findings failed to replicate using more stringent experimental controls and better data, and modern understandings of how brains work and our sense of self-perception forms and functions watered-down the idea that we (and our beliefs and behaviors) were simplistic enough to be understood by measuring our outwardly legible responses to (often leading) researcher questions.
That said, there's been renewed interest in this concept as digital technologies and communication mediums have made large-scale customization (presenting individualized messages to each person on the receiving end of a mass communication) feasible and widespread, once more raising the question of whether "magic bullet"-style messages might be feasible in contexts in which passive media consumption is the norm and critical thinking is seldom applied to the messages we consume (i.e. the way many people use social media).