The hypodermic needle theory suggests that the media has a direct and powerful effect on passive audiences by "injecting" ideas and views. It was popular in the 1940s-1950s when radio, TV, and ads first became widespread and were thought to influence behavior. The theory says the audience is powerless to resist media messages and will believe anything they see or hear. However, it is now seen as outdated since audiences are more media-literate and able to reject messages critically rather than just accepting everything passively.