The mind can absorb 20 images per second. Video runs at about 25 images per second. That means that for every second of TV or YouTube or any video, good or bad, well-intended or not, 5 images get implanted without our knowledge or consent.
Just start pounding an idea enough times into enough people until, hypnotically, they begin to believe it. Critical mass is achieved when the idea—no matter how false or ridiculous—becomes accepted as reality.