In The Matrix (1999), Neo takes the red pill to learn the truth about reality.
Morpheus offers Neo a choice between a blue pill and a red pill. The blue pill would return him to an ordinary life within the simulated world, while the red pill begins the process of freeing him from the Matrix. Neo chooses the red pill and awakens in the real world.
The scene made “red pill” and “blue pill” widely recognized cultural terms. The film uses the choice as a visual expression of uncertainty, freedom and the willingness to question accepted reality.
The pills are not literal computer programs that instantly explain everything. They are narrative devices in the film’s story, and the red pill leads to a difficult process of disconnection and recovery.