For example, when you are watching a horror movie, you feel the intense fear because of the sound effects, the darkness, the expression of fear in the actors' face, the color of the scenes etc.
In other words your lively envision seems almost real. The fear in you exists till you are in the movie theater. But when you com out, all the fear that seemed so real melt out and vanish. You realize that it was only a movie.
You do not believe it will happen to you, so you do not complete the second part of the [Law of Attraction] equation. (Abraham-Hicks)
Similarly, when you want something, in order to manifest it, you must fully believe in it coming to you. You should envision your mood when you have it in real. You should emotionally feel upbeat as if you are having it now like you were feeling all the emotions while watching the horror movie.In short, your thoughts should match you desire.
Read it again and again. Remember this sentence when you catch yourself thinking negatively.