Why directors make trailers?

Directors to film a movie they have to sing a lot of papers to make everything legal, and also they have to buy almost everything to make the best movie ever. When directors want to create a perfect movie and to win an award they have to make an excellent trailer, that´s why they make trailers, to make people to see the movie and to tell their friends to see it. If the trailer is good, people will want to see the entire movie. People just take like a picture at the first image that you are and when we talk about movies is the same, if we see for first time a movie or a trailer it must be mysterious, romantic, horrify, etc, to make it interesting and to want to see it. Each director is different and they think different, so for some directors’, trailers aren´t important but for others they are important. A trailer is like a summary of the movie that´s why some directors don´t like that people see trailers because they know everything that would happened in the movie and if they don´t like the trailer they never will see the movie.