Subliminal messages are those which messages which affect the subconscious mind of people. These messages affect a person without him or her knowing it. After a few repetitions of the messages in our ears or in front of eyes, these messages could have an important impact on the person's mind. The person may be inclined to do what is shown in the advertisement or in the movie.
Many companies employ publicity companies to create ads that use the subliminal messages in a bad way. Also, the movie makers exploit the inherent weakness of the audience and make their movies successful through these messages.
The advertisements try to attract people by using subliminal messages. Often they are related to sexual or romantic arousal of people. When it is related to children, these create an interest in the children through the feelings of pride, excitement, sarcaism etc. in the ad. The children are easily affected by the ads. Many people and children try to believe that they can also do similarly. But it is not advisable to do those stunts heroes do in the advertisements.
But subliminal messages do help education, memory, and learning of children and they can do better in their exams. In TV ads and in movies, there is a small text message printed at the bottom cautioning people not to repeat dangerous actions.